View source for Piccadilly line

{{short description|London Underground line}}
{{good article}}
{{Use British English|date=December 2021}}
{{Use dmy dates|date=May 2022}}
{{Infobox rail line
| name            = Piccadilly line
| logo            = London flag boxes - Underground Piccadilly line.svg
| logo_width      = 250px
| logo_alt        = 
| image           = RUSSELL SQUARE-14 020909 CPS (3998135457).jpg
| image_width     = 250px
| image_alt       = 
| caption         = A westbound Piccadilly line train to {{lus|Uxbridge}} at {{lus|Russell Square}} (2009)
| type            = [[Rapid transit]]
| system          = [[London Underground]]
| start           = Cockfosters
| mapcolour       = Dark blue
| mapcolourlink   = Tube map
| end             = {{cslist|Uxbridge|Heathrow Airport}}
| stations        = 53<ref name=tubemap>{{cite map/Standard Tube Map}}</ref>
| ridership2      = 217.995 million (2019)<ref>{{cite web |title=London Assembly Questions to the Mayor |url=https://www.london.gov.uk/who-we-are/what-london-assembly-does/questions-mayor/find-an-answer/tube-usage-1|publisher=London Assembly |year=2022 |access-date=29 February 2024}}</ref> passenger journeys
| open            = {{start date and age|1906|12|15|df=y}}
| lastextension   = 27 March 2008
| character       = Deep-level tube
| depot           = {{plainlist|
* [[Cockfosters Depot|Cockfosters]]
* [[Northfields Depot|Northfields]]
}}
| stock           = [[London Underground 1973 Stock|1973 Stock]]
| linelength      = {{convert|73.97|km|mi||abbr=on|order=flip}}
| tracklength     = 
| gauge           = {{track gauge|sg|allk=on}}
| electrification = {{630 V DC|conductor=fourth rail}}
| speed_mph       = 40-50
| website         = {{official URL}}
| map_name        = [[Transport for London]] {{nowrap|rail lines}}
| map             = {{London rail lines}}
| map_state       = collapsed
}}

The '''Piccadilly line''' is a [[Deep level underground|deep-level]] [[London Underground]] line running between the west and the north of [[London]]. It has two western branches which split at [[Acton Town tube station|Acton Town]] and serves 53 stations. The line serves [[Heathrow Airport]], and some of its stations are near tourist attractions in [[Central London]] such as [[Piccadilly Circus]] and [[Buckingham Palace]]. The [[District line|District]] and [[Metropolitan line|Metropolitan]] lines share some sections of track with the Piccadilly line. Printed in dark blue (officially "Corporate Blue", [[Pantone]] 072) on the [[Tube map]], it is the sixth-busiest line on the Underground network, with nearly 218 million passenger journeys in 2019.

The first section, between [[Finsbury Park station|Finsbury Park]] and [[Hammersmith tube station (District and Piccadilly lines)|Hammersmith]], was opened in 1906 as the [[Great Northern, Piccadilly and Brompton Railway]] (GNP&BR). The station tunnels and buildings were designed by [[Leslie Green]], featuring ox-blood [[terracotta]] facades with semi-circular windows on the first floor. When [[Underground Electric Railways of London]] (UERL) took over the line, it was renamed the Piccadilly line. Subsequent extensions were made to [[Cockfosters tube station|Cockfosters]], [[Hounslow West tube station|Hounslow West]] and [[Uxbridge tube station|Uxbridge]] in the early 1930s, when many existing stations on the Uxbridge and Hounslow branches were rebuilt to designs by [[Charles Holden]] of the Adams, Holden & Pearson architectural practice. These were generally rectangular, with brick bases and large tiled windows, topped with a [[concrete]] slab roof. The western extensions took over certain existing District line services, which were fully withdrawn in 1964.

Stations in central London were rebuilt to cater for a higher volume of passenger traffic. To prepare for the [[Second World War]], some stations were equipped with shelters and basic amenities, and others with [[blast wall]]s. Construction of the [[Victoria line]], the first section of which opened in 1968, helped to relieve congestion on the Piccadilly line; some sections of the Piccadilly had to be rerouted for [[cross-platform interchange]] with the new line. Several plans were made to extend the Piccadilly line to serve Heathrow Airport. The earliest approval was given in 1967, and the Heathrow extension opened in stages between 1975 and 1977. This served only Terminals 2 and 3 and the former Terminal 1. The line was extended again twice, to Terminal 4 via a loop in 1986, and to Terminal 5 directly from the main terminal station in 2008.

This line has two depots, at [[Northfields tube station|Northfields]] and Cockfosters, with a group of [[Siding (rail)|sidings]] at several locations. There are [[Crossover (rail)|crossovers]] at a number of locations, some of which allow trains to switch to different lines. The Piccadilly line's electric power was formerly generated at [[Lots Road Power Station]]. This was taken out of use in 2003, and the line is now powered from the [[National Grid (Great Britain)|National Grid network]]. [[London Underground 1973 Stock|1973 Stock]] trains are used on the line, 78 of which are needed to operate a 24 trains per hour (tph) service (a train every {{frac|2|1|2}} minutes) during peak hours. These trains are due to be replaced by [[London Underground 2024 Stock|2024 Stock]] in 2025.

==Route==
The Piccadilly line is a {{convert|73.97|km|mi|2|abbr=on|order=flip}} long north–west line, with two western branches splitting at [[Acton Town tube station|Acton Town]], serving 53 stations.<ref name=tubemap/><ref name=culgcalculations>Calculations were based on the mileage given in the reference. {{cite web |url=http://www.davros.org/rail/culg/piccadilly.html#layout |title=Piccadilly Line – Layout |work=Clive's Underground Line Guides |last=Feather |first=Clive |date=8 May 2020 |access-date=5 August 2020 |url-status=live |archive-url=https://web.archive.org/web/20200726113358/http://www.davros.org/rail/culg/piccadilly.html |archive-date=26 July 2020}}</ref> At the northern end, [[Cockfosters tube station|Cockfosters]] is a four-platform three-track terminus, and the line runs at surface level to just south of [[Oakwood tube station|Oakwood]]. [[Southgate tube station|Southgate station]] is in a tunnel, with tunnel portals to the north and south. Due to the difference in terrain, [[Arnos Park Viaduct|a viaduct]] carries the tracks through [[Arnos Park]] to [[Arnos Grove tube station|Arnos Grove]].{{sfn|Horne|2007|pp=78–79}} The line then descends into twin tube tunnels, passing through [[Wood Green tube station|Wood Green]], [[Finsbury Park tube station|Finsbury Park]] and central London. The central area contains stations close to tourist attractions, such as the [[London Transport Museum]], [[Harrods]], [[Buckingham Palace]] and [[Piccadilly Circus]].<ref>{{cite web |url=https://media.timeout.com/images/105275094/image.jpg |title=Out and about on the Piccadilly line |publisher=[[Transport for London]] |access-date=4 October 2020 |url-status=live |archive-url=https://web.archive.org/web/20201004100724/https://media.timeout.com/images/105275094/image.jpg |archive-date=4 October 2020}}</ref><ref>{{google maps |url=https://www.google.com.my/maps/place/Leicester+Square+Station/@51.5482801,-0.329954,28158m/data=!3m1!1e3!4m5!3m4!1s0x487604cd91e8c0f7:0xde0fdd0b8f9a7fcb!8m2!3d51.511451!4d-0.1281439?hl=en |title=Piccadilly line |access-date=4 October 2020}}</ref> The {{convert|15.3|km|mi|2|abbr=on|order=flip}} tunnel ends east of [[Barons Court tube station|Barons Court]], where the line continues west, parallel to the [[District line]], to Acton Town. A [[flying junction]], in use since 10 February 1910, separates trains going to the [[Heathrow Terminals 2 & 3 tube station|Heathrow]] branch from the [[Uxbridge tube station|Uxbridge]] branch.{{sfn|Horne|2007|p=46}}<ref name=piccfactstfl>{{cite web |url=https://tfl.gov.uk/corporate/modesoftransport/londonunderground/keyfacts/13175.aspx |title=Piccadilly line facts |publisher=[[Transport for London]] |access-date=20 August 2020 |url-status=dead |archive-url=https://web.archive.org/web/20140210035233/http://www.tfl.gov.uk/corporate/modesoftransport/londonunderground/keyfacts/13175.aspx |archive-date=10 February 2014}}</ref>

The Heathrow branch remains at surface level until the eastern approach to [[Hounslow West tube station|Hounslow West station]], where it enters a [[Tunnel|cut-and-cover tunnel]]. West of Hatton Cross, the line enters tube tunnels to [[Heathrow Airport]] and branches to the [[Heathrow Terminal 4 tube station|Terminal 4]] loop or to a terminus at [[Heathrow Terminal 5 station|Terminal 5]].{{sfn|Horne|2007|p=138}} On the Uxbridge branch, the line shares tracks with the District line between Acton Town and south of [[North Ealing tube station|North Ealing]]. Traversing terrain with cuttings and embankments, it continues to Uxbridge, sharing tracks with the [[Metropolitan line]] between [[Rayners Lane tube station|Rayners Lane]] and Uxbridge.{{sfn|Horne|2007|pp=43–44}} The distance between Cockfosters and Uxbridge is {{convert|31.6|mi|km|abbr=on}}.{{Sfn|Horne|2007|p=99}}

===Map===
[[File:Piccadilly Line.svg|750px|center|Geographically accurate path of the Piccadilly line]]

==History==
{{for|detailed histories of the Great Northern, Piccadilly & Brompton Railway (GNP&BR), the Great Northern & Strand Railway (GN&SR), and the Brompton & Piccadilly Circus Railway (B&PCR)|Great Northern, Piccadilly and Brompton Railway}}
The Piccadilly line began as the Great Northern, Piccadilly & Brompton Railway (GNP&BR), one of several railways controlled by the [[Underground Electric Railways Company of London]] (UERL), whose chief director was [[Charles Yerkes|Charles Tyson Yerkes]],{{sfn|Horne|2007|p=15}} although he died before the first section of the line opened. It currently runs on tracks built by The GNP&BR, the [[District Railway]] (DR) and the Metropolitan Railway (Met), and received major extensions in the 1930s and 1970s.

The GNP&BR was formed from the merger of two earlier, but unbuilt,{{sfn|Horne|2007|pp=6,8}} tube-railway companies taken over in 1901 by Yerkes's consortium: the Great Northern & Strand Railway (GN&SR) and the Brompton & Piccadilly Circus Railway (B&PCR).{{sfn|Horne|2007|p=10}} The GN&SR's and B&PCR's separate routes were linked with an additional section between {{lus|Piccadilly Circus}} and {{lus|Holborn}}. A section of the DR's scheme for a deep-level tube line between {{lus|South Kensington}} and {{lus|Earl's Court}} was also added in order to complete the route.{{refn|The original [[District Railway]] tube line was to be from Earl's Court to [[Mansion House tube station|Mansion House]]. It was intended to be an express route from South Kensington to Mansion House, with an intermediate station at [[Embankment tube station|Embankment]].<ref name="Gazette_03">{{London Gazette |date=22 November 1896 |issue=26797 |pages=6764–6767}}</ref>{{sfn|Horne|2007|p=7}}|group=note}} This finalised route, between [[Finsbury Park station|Finsbury Park]] and [[Hammersmith tube station (District and Piccadilly lines)|Hammersmith]] stations, was formally opened on 15 December 1906.{{sfn|Wolmar|2005|p=181}} On 30 November 1907, the short branch from Holborn to the Strand (later renamed {{lus|Aldwych}}) opened; it had been planned as the last section of the GN&SR before the amalgamation with the B&PCR.{{sfn|Horne|2007|pp=9,13,19}}

Initial ridership growth was low due to high use of new electric [[trams]] and motor buses. Financial stability was an issue, and as a result the company heavily promoted their railways via a new management team. UERL also agreed with other independent railway companies such as the [[Central London Railway]] (CLR, now part of the [[Central line (London Underground)|Central line]]) to jointly advertise a combined network known as the Underground.{{sfn|Horne|2007|p=32}}{{sfn|Badsey-Ellis|2005|pp=282–283}} On 1 July 1910, the GNP&BR and the other UERL-owned tube railways (the [[Baker Street and Waterloo Railway]] and the [[Charing Cross, Euston and Hampstead Railway]]) were merged by an [[act of Parliament]]{{which|date=July 2024}}<ref name=merge>{{London Gazette |date=23 November 1909 |issue=28311 |pages=8816–8818}}</ref> to become the ''[[London Electric Railway]] Company'' (LER).{{refn|The merger was carried out by transferring the assets of the CCE&HR and the BS&WR to the GNP&BR and renaming the GNP&BR as the London Electric Railway.{{sfn|Horne|2007|p=33}}|group=note}} The Underground railways still suffered financial issues,{{sfn|Wolmar|2005|pp=259–262}} and to address this, the [[London Passenger Transport Board]] was established on 1 July 1933.{{sfn|Wolmar|2005|p=266}}<ref name="LPTA">{{London Gazette |date=9 December 1930 |issue=33668 |pages=7905–7907}}</ref>

There were significant station layout changes in the 1910s and 1920s. On 4 October 1911, Earl's Court had new escalators installed connecting the [[District line|District]] and Piccadilly lines. They were the first to be installed on the Underground.{{sfn|Horne|2007|p=33}}{{sfn|Wolmar|2005|p=182}} On 10 December 1928, a rebuilt Piccadilly Circus station, designed by [[Charles Holden]],<ref name="eh_1226877">{{NHLE|num=1226877|desc=Piccadilly Circus Underground Station Booking Hall Concourse and Bronzework to Pavement Subway Entrances|access-date=2 August 2020}}</ref> was opened. This included a new booking hall located below ground and eleven escalators, replacing the original lifts.{{sfn|Horne|2007|p=39}}{{refn|The old street level station building closed on 21 July 1929.{{sfn|Lee|1966|p=23}}{{sfn|Horne|2007|p=39}}|group=note}}

One of the shafts at [[Holloway Road tube station|Holloway Road station]] was used as an experiment for [[Escalator#Alternative designs|spiral escalators]], but never used.{{sfn|Horne|2007|p=23}} An experiment to encourage passengers to step on the escalator three at a time at [[Manor House tube station|Manor House station]] was trialled.{{sfn|Horne|2007|p=82}} It failed due to opposition and potential dangers pointed out by the public.{{sfn|Horne|2007|p=82}}

===Extension to Cockfosters===
[[File:Ventilation panel, Wood Green tube station - geograph.org.uk - 1401101.jpg|thumb|One of the ventilation panels at Wood Green station platforms]]

While early plans to serve Wood Green (specifically [[Alexandra Palace railway station|Alexandra Palace]]) existed since the 1890s as part of the GN&SR,<ref name="Gazette_04">{{London Gazette |date=22 November 1898 |issue=27025 |pages=7040–7043}}</ref><ref name="Gazette_05">{{London Gazette |date=4 August 1899 |issue=27105 |pages=4833–4834}}</ref> this section to [[Finsbury Park station|Finsbury Park]] was later dropped from the GNP&BR proposal in 1902 when the GN&SR was merged with the B&PCR.{{sfn|Badsey-Ellis|2005|p=131}}{{sfn|Horne|2007|p=11}} In 1902, as part of an agreement for taking over the GN&SR, the [[Great Northern Railway (Great Britain)|Great Northern Railway]] (GNR) imposed a sanction<!--no suitable wikilink available--> on Yerkes to abandon the section north of Finsbury Park and they would construct the terminus below ground.{{sfn|Horne|2007|p=11}}{{sfn|Badsey-Ellis|2005|p=138}}{{sfn|Martin|2012|pp=182–183}}<ref name=hornsyhist1>{{cite web |url=https://hornseyhistorical.org.uk/piccadilly-line-extension-part-one/ |title=Part One |work=The Piccadilly Line Extension |last=Dean |first=Deadre |date=4 October 2019 |publisher=Hornsey Historical Society |access-date=5 August 2020 |url-status=live |archive-url=https://web.archive.org/web/20200806102029/https://hornseyhistorical.org.uk/piccadilly-line-extension-part-one/ |archive-date=6 August 2020}}</ref> Finsbury Park remained as an overcrowded terminus of the line, and was described as "intolerable". Many passengers arriving at both stations had to change onto buses, trams, and [[suburban rail]] services to complete their journeys further north.{{sfn|Horne|2007|p=91}}{{refn|The diagram in the reference shows bus or tram routes in the north which were in close proximity to Finsbury Park.|group=note}} The GNR attempted to address this issue by considering [[electrification]] several times, but to no avail due to shortage of funds. Meanwhile, the LER proposed an extension in 1920 but was [[wikt:overrule#Verb|overruled]] by the GNR, which was widely regarded as "unreasonable". In 1923, a petition by the Middlesex Federation of Ratepayers to [[repeal]] the 1902 act of Parliament{{which|date=July 2024}} emerged. It was reported that a "fierce exchange of arguments" occurred during a parliamentary session in March 1924 to request this change.<ref>{{cite web |url=https://hansard.parliament.uk/Commons/1924-03-05/debates/3693b732-edd8-43ac-b586-573bf88e0a0d/LondonAndNorthEasternRailwayBill(ByOrder) |title=London and North Eastern Railway Bill (By Order) |publisher=Hansard Parliament UK |date=15 March 1924 |access-date= 6 August 2020 |url-status=live |archive-url=https://web.archive.org/web/20200806101549/https://hansard.parliament.uk/Commons/1924-03-05/debates/3693b732-edd8-43ac-b586-573bf88e0a0d/LondonAndNorthEasternRailwayBill%28ByOrder%29 |archive-date=6 August 2020}}</ref><ref name=hornsyhist1/> [[Frank Pick]], as the new assistant managing director of the Underground, distributed photographs of the congestion at Finsbury Park to the press. All of this pressure finally prompted the government to initiate "The North and North-East London Traffic Inquiry", with initial reports only recommending a one-station extension to [[Manor House tube station|Manor House]]. The [[London and North Eastern Railway]] (LNER), being the successor of the GNR, was placed in the position of electrifying its own services or withdrawing its [[veto]] of an extension of the Piccadilly line. With funds still being insufficient to electrify the railway, the LNER reluctantly agreed to the latter.{{sfn|Martin|2012|pp=182–183}} An extension was highly likely at this stage, based on a study in October 1925 by the [[London and Home Counties Traffic Advisory Committee|London & Home Counties Traffic Advisory Committee]].{{sfn|Horne|2007|p=65}}{{sfn|Wolmar|2005|pp=227–231}}

{{Infobox UK legislation
| short_title           = London Electric Metropolitan District Central London and City and South London Railway Companies Act 1930
| type                  = Act
| parliament            = Parliament of the United Kingdom
| long_title            = 
| year                  = 1930
| citation              = [[20 & 21 Geo. 5]]. c. lxxxviii
| introduced_commons    = 
| introduced_lords      = 
| territorial_extent    = 
| royal_assent          = 4 June 1930
| commencement          = 
| expiry_date           = 
| repeal_date           = 
| amends                = 
| replaces              = 
| amendments            = 
| repealing_legislation = 
| related_legislation   = 
| status                = 
| legislation_history   = 
| theyworkforyou        = 
| millbankhansard       = 
| original_text         = https://www.legislation.gov.uk/ukla/Geo5/20-21/88/pdfs/ukla_19300088_en.pdf
| revised_text          = 
| use_new_UK-LEG        = 
| UK-LEG_title          = 
| collapsed             = yes
}}
Pick, together with the Underground board, began working on the extension proposal. Much pressure was also received from a few districts such as [[Tottenham]] and [[Harringay]], but it was decided that the optimal route would be the midpoint of the GNR and the [[Lea Valley lines|Hertford Line]].{{refn|An interchange at Manor House was provided instead for connecting trams to [[Edmonton, London|Edmonton]], Tottenham and [[London Borough of Enfield|Enfield]] East.{{sfn|Horne|2007|p=65}}|group=note}} This was backed by the committee, and parliamentary approval for the extension was obtained on 4 June 1930, under the '''{{visible anchor|London Electric Metropolitan District Central London and City and South London Railway Companies Act 1930}}''' ([[20 & 21 Geo. 5]]. c. lxxxviii).<ref>{{London Gazette |date=6 June 1930 |issue=33613 |pages=3561}}</ref><ref name=hornsyhist2>{{cite web |url=https://hornseyhistorical.org.uk/piccadilly-line-extension-part-two/ |title=Part Two |work=The Piccadilly Line Extension |last=Dean |first=Deadre |date=18 January 2020 |publisher=Hornsey Historical Society |access-date=5 August 2020 |url-status=live |archive-url=https://web.archive.org/web/20200806101853/https://hornseyhistorical.org.uk/piccadilly-line-extension-part-two/ |archive-date=6 August 2020}}</ref>{{refn|LNER continued to oppose the decision, and promised to electrify the line if the extension was rejected.{{sfn|Horne|2007|p=66}}<ref name=hornsyhist1/>|group=note}} Funding was obtained from legislation under the Development (Loan Guarantees and Grants) Act 1929 ([[20 & 21 Geo. 5]]. c. 7) instead of the [[Trade Facilities Act]]. The extension would pass through [[Manor House, London|Manor House]], [[Wood Green]] and [[Southgate, London|Southgate]], ending at Enfield West (now [[Oakwood tube station|Oakwood]]);{{sfn|Horne|2007|pp=65–66}}{{refn|It was intended for the station to be named East Barnet, but was quickly renamed before opening. Alternative suggestions were Merryhills and Oakwood. The station was gradually renamed, to Enfield West (Oakwood) on 3 May 1934, and to its present name on 1 September 1946.{{sfn|Horne|2007|pp=68,73}}{{sfn|Harris|2006|p=53}}|group=note}} based on the absence of property development along the line. In November 1929, the projected terminus was shifted further north to [[Cockfosters tube station|Cockfosters]] to accommodate a larger depot. It was estimated that ridership on the extension, which would cost £4.4&nbsp;million, would be 36 million passengers a year.{{sfn|Horne|2007|p=66}} In addition to Enfield West, stations were designated at [[Southgate tube station|Southgate]], [[Arnos Grove tube station|Arnos Grove]], [[Bounds Green tube station|Bounds Green]], [[Wood Green tube station|Wood Green]], [[Turnpike Lane tube station|Turnpike Lane]], and Manor House. Bounds Green station was almost cancelled in order to improve journey times.{{sfn|Horne|2007|p=70}} A more expensive provision was rejected, which included construction of a third track between Finsbury Park and Wood Green. Furthermore, since journey speed was a primary consideration in decision-making for the extension, the pencilled-in and much lobbied-for additional station near the corner of Green Lanes and St. Ann's Road in [[Harringay]] was dropped.{{sfn|Horne|2007|pp=68–70}}<ref name=hornsyhist2/>

Tunnel rings, cabling and [[concrete]] were produced in Northern England, while unemployed industrial workers there helped in the construction of the extension. Construction of the extension started quickly, with the boring of the twin tube tunnels between Arnos Grove and Finsbury Park proceeding at the rate of a mile per month. Twenty-two tunnelling shields were used for the tunnels,{{sfn|Martin|2012|pp=181–182}} and tunnel diameters were slightly larger than the old section, at {{convert|12|ft|m|abbr=on}}. Sharp curves were also avoided to promote higher average speeds on the extension. Platforms {{convert|400|ft|m|abbr=on}} long were originally planned for each station to fit 8-car trains, but were cut short to {{convert|385|ft|m|abbr=on}} when built. Some stations were also built with wider platform tunnels to cater to expected high patronage. To connect with buses and trams, interchange stations were provided with exits which led passengers directly to the bus terminal or tram stop from the subsurface ticket hall. The exits were purposed to improve connections which avoided chaotic passenger flow such as at Finsbury Park. Wood Green was an exception due to engineering difficulties, with the ticket hall at street level instead. Ventilation shafts were provided at Finsbury Park Tennis Courts, Colina Road and Nightingale Road, supplementing the existing fans within the stations. Provisions for future branch lines to [[Enfield, London|Enfield]] and Tottenham were made at Wood Green and Manor House respectively, both to have reversing sidings. This had since changed, with only a reversing siding built at Wood Green and no provision for the branch line. Arnos Grove was built to have four platforms facing three tracks for trains to reverse regularly, with seven stabling sidings instead of one reversing siding and two platforms.{{sfn|Horne|2007|pp=69,74–75,86}}<ref>{{cite web |url=https://www.google.com/maps/place/Arnos+Grove/@51.61645,-0.13304,17z/data=!3m1!4b1!4m2!3m1!1s0x48761973b6a2cc5f:0x3f182b0278779adc |title=Arnos Grove tube station |website=Google Maps |access-date=5 August 2020}}</ref><ref name=cartomap>{{cite map |url=http://cartometro.com/documents/CartoMetroLondon.v3.9.pdf?r=cmf |format=PDF |title=Greater London Transport Tracks Map |work=CartoMetro London Edition |version=3.9 |last=Jarrier |first=Franklin |url-status=live |archive-url=https://web.archive.org/web/20200823123452/http://cartometro.com/documents/CartoMetroLondon.v3.9.pdf?r=cmf |archive-date=23 August 2020 |access-date=23 August 2020}}</ref>

Most of the tunnelling works were completed by October 1931, with the Wood Green and Bounds Green station tunnels done by the end of the year.<ref name=hornsyhist2/> The first phase of the extension to Arnos Grove opened on 19 September 1932, without ceremony. The line was further extended to Enfield West on 13 March 1933 and finally to Cockfosters on 31 July 1933, again without ceremonies.{{sfn|Wolmar|2005|pp=227–231}}{{sfn|Rose|1999}} The total length of the extension was {{convert|12.3|km|mi|abbr=on|order=flip}}.<ref name=culgcalculations/> Free tickets were distributed to residents on the first days of service on each extension. Initial ridership was 25&nbsp;million at the end of 1933, which sharply increased to 70&nbsp;million by 1951.{{sfn|Horne|2007|p=100}} Despite there being no official opening ceremonies, [[Edward VIII|the Prince of Wales]] visited the extension on 14 February 1933.{{sfn|Horne|2007|pp=90–92}}{{refn|He travelled from Piccadilly Circus to Wood Green, and back to [[Hyde Park Corner tube station|Hyde Park Corner]] for inspection.{{sfn|Horne|2007|p=92}}|group=note}}

===Westward extensions===
The [[Hounslow West tube station|Hounslow West]] (then Hounslow Barracks) extension of the Piccadilly line, together with the [[Uxbridge]] extension, aimed to improve services on the [[District line]] which at the time were serving both branches from [[Acton Town tube station|Acton Town]] (then Mill Hill Park).{{sfn|Horne|2007|p=42}}{{refn|The Hounslow & Metropolitan Railway originally opened a shuttle service between Mill Hill Park and [[Hounslow Town tube station|Hounslow Town]] on 1 May 1883, with a single-track branch to Hounslow Barracks which opened on 21 July 1884. The route to Hounslow Town eventually closed on 2 May 1909. The District Railway took over the branches in 1903.{{sfn|Horne|2007|pp=42,46}}|group=note}} The Uxbridge extension followed along existing routes on the DR and Met. The DR opened a spur from [[Ealing Common tube station|Ealing Common]] to [[South Harrow tube station|South Harrow]] in June 1903. The Met opened its extension to Uxbridge in July 1904.{{sfn|Horne|2007|pp=42–45}} Through trains of the DR were eventually extended to Uxbridge on 1 March 1910, henceforth sharing tracks with the Met between [[Rayners Lane tube station|Rayners Lane]] and Uxbridge.{{sfn|Horne|2007|pp=44–45}}{{refn|The Ealing & South Harrow Railway (E&SHR) was approved in 1894 and completed in 1899 after approximately a two-year construction period. Insufficient funds from the DR delayed its opening. On the other hand, the [[Harrow & Uxbridge Railway]] (H&UR) was proposed in 1896 and authorised a year later.{{sfn|Simpson|2003|p=97}} The Met offered to fund the line, with conditions to take over the Rayners Lane to [[Uxbridge tube station|Uxbridge]] section of the H&UR. Agreement was reached in 1899, with the Met also constructing the connection from South Harrow to Rayners Lane, whilst allowing up to three trains an hour from the DR between South Harrow and Uxbridge.{{sfn|Horne|2003|p=26}} Construction began in 1901, and the Met opened its extension to Uxbridge on 4 July 1904.{{sfn|Horne|2007|pp=42–45}}|group=note}}

The viaduct from Studland Road Junction west of Hammersmith to [[Turnham Green tube station|Turnham Green]] was quadrupled on 3 November 1911. The [[London and South Western Railway]] (L&SWR) used the northern pair of tracks while the District Railway used the southern pair.{{sfn|Horne|2007|pp=46–47}} The LER proposed an extension in November 1912 to [[Richmond station (London)|Richmond]] due to available capacity to the west and the fact that passenger interchanges were large at Hammersmith. It would connect with the L&SWR tracks at Turnham Green.<ref>{{London Gazette |date=22 November 1912|issue=28665|pages=8798–8801}}</ref> It was approved as the [[London Electric Railway Act 1913]] ([[3 & 4 Geo. 5]]. c. xcvii) on 15 August 1913,<ref>{{London Gazette|date=19 August 1913|issue=28747|pages=5929–5931}}</ref> but [[World War I]] resulted in no works done on the extension.{{sfn|Horne|2006|p=56}} A parliamentary report of 1919 recommended through running to Richmond and [[Ealing]].{{sfn|Barker|Robbins|1974|p=252}} The Richmond extension plan was revived in 1922 by [[Albert Stanley, 1st Baron Ashfield|Lord Ashfield]], the Underground's chairman. It was decided that the Piccadilly line extension was favourable over the CLR's as it was cheaper and had more capacity available.{{sfn|Horne|2007|pp=48–49}}{{refn|The CLR also had its Richmond extension proposal passed on the same day as the LER's. Nothing was done either.{{sfn|Horne|2007|p=48}} The L&SWR section ceased operation in 1916 and its ownership was transferred to the [[Southern (Govia Thameslink Railway)|Southern Railway]] in 1923.{{sfn|Horne|2006|p=55}} The CLR, by the 1920s, had capacity constraints due to increased patronage from Ealing and congestion in the central section.{{sfn|Horne|2007|pp=48–49}}|group=note}} By 1925, the [[District line]] was running out of capacity west of Hammersmith, where services were headed to South Harrow, Hounslow Barracks, Richmond and [[Ealing Broadway station|Ealing Broadway]]. Demand was also low on the South Harrow branch because of infrequent services and competition among other rail lines in the vicinity of each station. This prompted the Piccadilly line extension to be an express service between Hammersmith and Acton Town, with the future [[Heathrow Airport]] extension safeguarded in 40 years' time.{{sfn|Horne|2007|p=51}} The Piccadilly line would run on the inner pair of tracks, and the District line on the outer.{{sfn|Barker|Robbins|1974|p=252}} Permission was granted to quadruple tracks to Acton Town in 1926 in conjunction with permit renewal for the extension. The Richmond extension never happened, but provisions allocated would allow this option to be revisited later.{{sfn|Horne|2007|pp=51,52}} Extensions would instead be to Hounslow Barracks and South Harrow, taking over DR services to the latter, with an estimated cost of £2.3&nbsp;million.{{sfn|Horne|2007|pp=50–51,66}}{{refn|The District line instead focused on running trains to Richmond, Ealing Broadway and [[Wimbledon station|Wimbledon]], with the South Harrow to Uxbridge and Acton Town to [[South Acton railway station (England)|South Acton]] shuttles to remain. In October 1930, provision was also made to have rush hour DR services to South Harrow.{{sfn|Horne|2006|pp=52,56}}|group=note}} In 1930, unsuccessful negotiations were made between LER and the Met to extend Piccadilly line trains to Rayners Lane for passengers to change trains.{{sfn|Horne|2007|p=58}}

In 1929, quadrupling was to extend to [[Northfields tube station|Northfields]] for express trains to terminate there. This work was completed on 18 December 1932. Overall works for the extension began in 1931, approximately a year after permission was granted and funded under the Development (Loan Guarantees and Grants) Act 1929 ([[20 & 21 Geo. 5]]. c. 7). The Studland Road Junction area was partially rebuilt, with some of the old viaducts retained to date. The junctions diverging to Richmond were reconfigured at Turnham Green. Reversing facilities were initially designated at the latter, but these were not built.{{sfn|Horne|2007|p=52}} Trial runs of Piccadilly line trains began on 27 June 1932. On 4 July 1932, services were extended to South Harrow, which replaced DR services. Northfields services were introduced on 9 January 1933, and on 13 March, were extended to Hounslow West. On 1 July 1933, the [[London Passenger Transport Board]] (LPTB) was formed, which included the Met, the DR and LER.{{sfn|Wolmar|2005|p=266}} The board decided that there was sufficient demand to run through trains to Uxbridge due to rapidly developing suburbs along the line. The extension of Piccadilly line trains to Uxbridge began on 23 October 1933, but with many trains still reversing at South Harrow. By then, most Piccadilly line trains continued beyond Hammersmith, and District line trains to Hounslow were reduced to off-peak shuttles to Acton Town. An enhanced off-peak Piccadilly line service was introduced on 29 April 1935, cutting off-peak District line services down to the Acton Town–[[South Acton railway station (England)|South Acton]] shuttle.{{sfn|Horne|2006|p=60}} South Harrow short trips proved to be an inconvenience. The solution was to move reversing facilities to Rayners Lane. A new reversing siding was built there in 1935, which allowed some peak hour trains to terminate beginning in May 1936. Regular reversals were fully implemented in October 1943.{{sfn|Horne|2007|pp=54,57–58}} Peak-hour District line trains to Hounslow were fully withdrawn on 9 October 1964.{{sfn|Horne|2006|p=88}}

===Modernisation, World War II and Victoria line===
In conjunction with the new extensions, several stations were considered for closure to increase overall line speeds. [[Down Street tube station|Down Street]] closed on 21 May 1932, [[Brompton Road tube station|Brompton Road]] on 29 July 1934, and [[York Road tube station|York Road]] on 17 September 1932.{{sfn|Rose|1999}}{{sfn|Lee|1966|p=22}} All three stations were lightly used. Down Street and Brompton Road were replaced, respectively, by relocated entrances at [[Hyde Park Corner tube station|Hyde Park Corner]] and [[Knightsbridge tube station|Knightsbridge]]. Knightsbridge's new below-ground ticket hall required stairwells from the entrance, one of which took over part of the Barclays Bank branch there. Both of the latter two stations retained their existing platforms, but the access from the surface was reconstructed with their entrances closer to the closed stations. These new entrances were provided with escalators, which replaced the lifts, improving passenger circulation. The Aldwych branch was deemed unprofitable. In 1929, an extension to [[Waterloo tube station|Waterloo]] was approved, costed at £750,000, but no progress was made on its construction. Dover Street (now [[Green Park tube station|Green Park]]), [[Leicester Square tube station|Leicester Square]] and [[Holborn tube station|Holborn]] stations received new sets of escalators, the latter having four in a single shaft. These were completed in the early 1930s.{{sfn|Badsey-Ellis|2016|p=212}}<ref>{{cite web |url=http://www.architecture.com/LibraryDrawingsAndPhotographs/Exhibitionsandloans/VARIBAArchitecturePartnershipexhibitions/UndergroundJourneys/Holdenesque/LeicesterSquare.aspx |title=Underground Journeys: Leicester Square |publisher=[[Royal Institute of British Architects]] |archive-url=https://web.archive.org/web/20110707160725/http://www.architecture.com/LibraryDrawingsAndPhotographs/Exhibitionsandloans/VARIBAArchitecturePartnershipexhibitions/UndergroundJourneys/Holdenesque/LeicesterSquare.aspx |archive-date=7 July 2011 |url-status=dead |df=dmy-all |access-date=11 August 2020}}</ref><ref>{{cite web |url=https://www.flickr.com/photos/36844288@N00/4490232964 |title=Architectural Plan and Elevation |publisher=London Passenger Transport Board |year=1933 |access-date=11 August 2020 |url-status=live |archive-url=https://web.archive.org/web/20200811131255/https://www.flickr.com/photos/36844288@N00/4490232964 |archive-date=11 August 2020}}</ref> As part of the 1935–40 [[New Works Programme]], Earl's Court was largely reconstructed at street level. At [[King's Cross St Pancras tube station|King's Cross St Pancras]], the Piccadilly and Northern lines were finally connected via new escalators, albeit with construction delayed due to financial difficulties.{{sfn|Day|Reed|2010|p=131}}{{refn|The four escalators led passengers down from the ticket hall to the new Central line concourse, and a further three to the Piccadilly line concourse.{{sfn|Horne|2007|p=96}}|group=note}} As a result, [[Russell Square tube station|Russell Square]] station retained its lifts.{{sfn|Horne|2007|pp=92–96}}

To prepare for the [[Second World War]], several stations had [[blast wall]]s added. Others, such as Green Park, Knightsbridge and King's Cross St Pancras, had floodgates installed. The line was also involved in the evacuation of 200,000 children, by transporting them towards both ends of the line, then transferring them to main line trains to continue their journeys to different country distribution hubs.{{sfn|Horne|2007|pp=103–106}} Some underground stations were fitted with [[bunk bed]]s, toilets and first aid facilities, and [[sewerage]]. The disused Down Street was converted to an underground [[bunker]] for government use.{{sfn|Connor|2006|p=33}} Other stations such as Holborn and Earl's Court also had essential wartime uses. The former had the Aldwych branch platforms as the wartime engineering quarters whilst the branch service was temporarily closed.{{sfn|Connor|2001|pp=98–99}} The latter produced [[Torpedo Data Computer]]s at the transfer concourse between the District and Piccadilly lines.{{sfn|Horne|2007|pp=103–106}} Aldwych station was used as storage for [[British Museum]] exhibits.{{sfn|Connor|2001|pp=98–99}} On 13 October 1940, a bomb explosion caused the westbound platform tunnel at Bounds Green station to collapse, killing nineteen shelterers. Train services were suspended for two months.{{sfn|Horne|2007|p=105}}<ref name=blitz>{{cite web |url=http://www.bowesandbounds.org/profiles/blogs/bounds-green-and-the-blitz |last=Richard |first=McKeever |title=Bounds Green and the Blitz |publisher=Bowes and Bounds Connected |date=7 September 2010 |access-date=13 November 2020 |archive-date=9 May 2015 |url-status=live |archive-url=https://web.archive.org/web/20150509120225/http://www.bowesandbounds.org/profiles/blogs/bounds-green-and-the-blitz}}</ref>

[[File:Finsbury Park station Platform Changes.png|thumb|upright=1.35|Reconfiguration of tunnels and platforms at Finsbury Park]]

In preparation for the [[Victoria line]], [[cross-platform interchange]] was to be provided at a few stations, which included Finsbury Park on the Piccadilly line.{{sfn|HMSO|1959|p=13}} This meant that the Piccadilly line had to be realigned there, and the [[Northern City line]] platforms, being parallel to the existing Piccadilly line platforms, were to be transferred to the pair of lines. The Northern City line would be redirected to the surface platforms. The westbound Piccadilly line track would be rerouted onto one of these platforms, with the southbound Victoria line using the other. The northbound Victoria line would reuse the old westbound Piccadilly line platform and a part of the old tunnels, with the Piccadilly line diversion tunnels spanning {{convert|3150|ft|m|abbr=on}}.{{sfn|Horne|2007|p=113}}

Construction of the diversion began in October 1964, with the Northern City line having a temporary closure.{{sfn|Day|Reed|2010|p=163}} At the northern junction, step plate [[Junction (rail)|junctions]] were built to divert the existing line when the new tunnels were complete. They were fitted into the original Northern City line tunnels which had a greater tunnel diameter until two running tunnels were able to merge. The old and unused running tunnel was disconnected and blocked off when the junction tunnel was near its completion. Alteration of temporary [[Points (rail)|points]] junctions and shifting of signals completed the diversion tunnels. In the south, the Piccadilly would be diverted to descend sharply under the northbound Victoria line tunnel, and then ascending to the original level which had a difference of {{convert|5|ft|m|abbr=on}} approximately {{convert|200|ft|m|abbr=on}} north of [[Arsenal tube station|Arsenal station]]. The old westbound tunnel had to be supported on a [[Trestle support|trestle]] for works to be done. The trestle and old tracks were entirely removed once the diversion was ready for switchover. New tracks were laid at a rapid rate; it was done in about thirteen hours on 3 October 1965.{{sfn|Horne|2007|p=113}} Both lines were connected via junctions south of Finsbury Park for stock movement and engineering trains. It was intended for Green Park to have cross-platform interchange, but was deemed impossible due to the lines crossing at right angles. The Victoria line opened on 1 September 1968 from [[Walthamstow Central tube station|Walthamstow Central]] to [[Highbury & Islington station|Highbury & Islington]] via Finsbury Park, and on 7 March 1969 to [[Warren Street tube station|Warren Street]] via King's Cross St Pancras,{{sfn|Day|Reed|2010|p=166}} providing relief to the Piccadilly line.{{sfn|Horne|2007|p=114}}

===Extension to Heathrow Airport===
[[File:LU1973 Refurbished Interior.jpg|thumb|upright=1.35|Inside a Piccadilly line car]]
To cater to the rapid growth of road traffic to [[Heathrow Airport]], several rail lines were considered to serve the airport. An average increment of 1 million passengers a year between 1953 and 1973, and rising issues with airline [[Coach (bus)|coach]] services from major terminals due to location, traffic congestion, larger aircraft capacity and increasing leisure travel further increased the need for public transport connections. Other than the Piccadilly line extension from [[Hounslow West tube station|Hounslow West]],{{refn|The four-tracking extension to [[Hounslow East tube station|Hounslow East]] from Northfields was considered in the 1940s to allow Heathrow express trains to run fast into central London. Another express rail link planned by LPTB would terminate at Hyde Park or Earl's Court, which would have costed £5–12&nbsp;million.{{sfn|Horne|2007|pp=117–118}}|group=note}} a [[Southern Railway (UK)|Southern Railway]] spur (section now transferred to part of [[South Western Railway (train operating company)|South Western Railway]]) from [[Feltham railway station|Feltham]] was also contemplated. These schemes were brought into parliamentary discussion in November 1966, and were approved with [[royal assent]] as the London Transport Act 1967 (c. xxxix) and British Railways Act 1967 (c. xxx) respectively on 27 July 1967.<ref>{{London Gazette |date=1 August 1967 |issue=44377 |pages=8450}}</ref> Partial government funding was obtained in April 1972 for the {{convert|3.5|mi|km|abbr=on}} Piccadilly line extension, and the estimated cost of construction was £12.3&nbsp;million.{{sfn|Horne|2007|pp=115–120}}

On 27 April 1971, a construction ceremony was launched by Sir [[Desmond Plummer]], leader of the [[Greater London Council]], by bulldozing "the first [[sod]]". Platforms at Hounslow West had to be relocated below-ground to the north of the existing for the new track alignment. The 1931 ticket hall was retained, with connections to the new platforms. A [[Tunnel#Cut-and-cover|cut-and-cover]] excavation method was used between Hounslow West and [[Hatton Cross tube station|Hatton Cross]], a new station on the extension. This 2-mile section had a shallow [[trench]] dug, with the tunnel walls supported by intersecting [[Deep foundation|concrete piles]]. The line had to cross the [[River Crane, London|River Crane]] just east of Hatton Cross; therefore it emerges briefly on a bridge, with the two portals having concrete retaining walls. Deep tube tunnels were bored from Hatton Cross to [[Heathrow Terminals 2 & 3 tube station|Heathrow Central]] (now Heathrow Terminals 2 & 3). On 19 July 1975, the line was extended to Hatton Cross.{{sfn|Day|Reed|2008|p=178}}{{refn|Several coach services were redirected to this station from Hounslow West.{{sfn|Horne|2007|p=121}}|group=note}} The Heathrow Central extension was inaugurated by [[Elizabeth II|the Queen]] around noon on 16 December 1977, with revenue services commencing at 3pm.{{sfn|Horne|2007|pp=120–121}}

In the 1970s, planning was already underway for a [[Heathrow Terminal 4|fourth terminal]] for the airport, and its location was to be to the southeast of the existing terminals. As the Piccadilly line's route to the existing terminals was out of place, a loop track was adopted as the best method to serve the new terminal. The westbound track between Hatton Cross and Heathrow Central would be retained for emergency services. Approval for [[Heathrow Airport Holdings|British Airport Authority]] (BAA) to construct the fourth terminal was granted in 1979.<ref name=":03">{{Cite news |last=Cobley |first=Jim |date=28 March 1986 |title=Royals "Fly the Tube" as Heathrow plugs in |work=LRT News |pages=4–5}}</ref> Permissions for constructing for the loop was approved and received royal assent under the London Transport Act 1981 (c. xxxii) on 30 October 1981.<ref>{{London Gazette |date=5 November 1981 |issue=48785 |pages=14033}}</ref> The [[station box]] would be built by BAA as part of the £200 million construction cost of the new terminal. By 1982, construction of the fourth terminal building was behind schedule, and in July 1982 the location of [[Heathrow Terminal 4 tube station|the station]] was moved from below the terminal building to a nearby car park. Construction of the {{convert|2.5|mi|km|abbr=on}} extension began on 9 February 1983, with an estimated cost of £24.6&nbsp;million. Tunnelling for the loop was completed in seventeen months. It was expected that the extension would open with the new terminal. However, the terminal opening was delayed, with the loop service completed and commissioned on 4 November 1985.<ref name=":02">{{Cite news |last=Cobley |first=Jim |date=28 March 1986 |title=Royals "Fly the Tube" as Heathrow plugs in |work=LRT News |pages=4–5}}</ref> The terminal and station were finally opened a few months later on 1 April 1986, by the [[Charles, Prince of Wales|Prince]] and [[Diana, Princess of Wales|Princess of Wales]]. Regular traffic began twelve days later with trains serving Terminal 4 via a one-way loop to Terminals 1,2,3.{{sfn|Horne|2007|pp=125–126}} The station only has a single platform, the only one with this configuration on the Piccadilly line.<ref name=cartomap/>

[[Heathrow Terminal 5 station|Terminal 5]] required another extension, funded by BAA. However, its proposed alignment caused an issue: it was reported that London Underground was unhappy with the terminal's location on the site of the old [[Perry Oaks]] sludge works which was originally intended for Terminal 4.{{sfn|Horne|2007|p=138}} It was now impossible for all three terminals to be served on the same route, and the final solution was to have twin tunnels serving Terminal 5 from Terminals 1,2,3. From 7 January 2005 until 17 September 2006, the loop via Terminal 4 was closed to allow this connection to be built. Terminals 1,2,3 became a temporary terminus; shuttle buses served Terminal 4 from the Hatton Cross bus station.{{sfn|Horne|2007|pp=137–138}} Part of the junction between the through and loop tracks needed to be rebuilt. The Terminal 5 project team shut down two [[Hangar|aircraft stand]]s from Terminal 3 so that an access shaft could be constructed. The new junction was then built into a concrete box which connected all the underground tunnels.<ref>{{cite press release |url=https://tfl.gov.uk/info-for/media/press-releases/2006/september/tube-one-step-closer-for-heathrow-terminal-5 |title=Tube One Step Closer for Heathrow Terminal 5 |date=14 September 2006 |access-date=17 August 2020 |publisher=[[Transport for London]] |url-status=live |archive-url=https://web.archive.org/web/20200817145027/https://tfl.gov.uk/info-for/media/press-releases/2006/september/tube-one-step-closer-for-heathrow-terminal-5 |archive-date=17 August 2020}}</ref> The station and terminal were opened on 27 March 2008, splitting westbound Piccadilly line services into two: one via the Terminal 4 loop, another direct to Terminal 5.<ref name=heathrowt5pressrelease>{{cite press release |url=https://tfl.gov.uk/info-for/media/press-releases/2008/march/first-piccadilly-line-passengers-travel-to-heathrow-terminal-5 |title=First Piccadilly Line Passengers Travel to Heathrow Terminal 5 |date=27 March 2008 |access-date=17 August 2020 |publisher=[[Transport for London]] |url-status=live |archive-url=https://web.archive.org/web/20200817150229/https://tfl.gov.uk/info-for/media/press-releases/2008/march/first-piccadilly-line-passengers-travel-to-heathrow-terminal-5 |archive-date=17 August 2020}}</ref><ref name=culgpiccadilly>{{cite web |url=http://www.davros.org/rail/culg/piccadilly.html |title=Piccadilly Line |work=Clive's Underground Line Guides |last=Feather |first=Clive |date=8 May 2020 |access-date=17 August 2020 |url-status=live |archive-url=https://web.archive.org/web/20200726113358/http://www.davros.org/rail/culg/piccadilly.html |archive-date=26 July 2020}}</ref>

===Aldwych branch closure===
{{for|detailed explanation of the Aldwych branch|Aldwych tube station}}
Plans to extend the Aldwych branch south to Waterloo were revived several times during the station's life. The extension was considered in 1919 and 1948, but no progress towards constructing the link was made.{{sfn|Connor|2001|pp=98–99}}

In the years after the Second World War, a series of preliminary plans for relieving congestion on the London Underground had considered various east–west routes through the Aldwych area, although other priorities meant that these were never proceeded with. In March 1965, a [[British Railways Board|British Rail]] and [[London Transport Board|London Transport]] joint planning committee published "A Railway Plan for London", which proposed a new tube railway, the [[Fleet line]] (later renamed the [[Jubilee line]]), to join the [[Bakerloo line]] at {{stl|London Underground|Baker Street}} then run via Aldwych and into the City of London before heading into south-east London. An interchange was proposed at Aldwych and a second recommendation of the report was the revival of the link from Aldwych to Waterloo.{{sfn|Horne|2000|pp=31–33}}<ref name="railarch">{{cite book |url=https://www.railwaysarchive.co.uk/documents/BRLT_RailwayPlanForLondon1965.pdf |title=A Railway Plan for London |date=March 1965 |author=[[British Railways Board]]/[[London Transport Board]] |page=23 |access-date=31 October 2020 |url-status=live |archive-date=30 August 2020 |archive-url=https://web.archive.org/web/20200830122021/https://www.railwaysarchive.co.uk/documents/BRLT_RailwayPlanForLondon1965.pdf}}</ref> London Transport had already sought parliamentary approval to construct tunnels from Aldwych to Waterloo in November 1964,<ref name="notices">{{cite journal |date=3 December 1964 |title=Parliamentary Notices |journal=[[The Times]] |issue=56185 |pages=2 |url=http://infotrac.galegroup.com/itw/infomark/322/785/116929157w16/purl=rc1_TTDA_0_CS33777539&dyn=17!xrn_1_0_CS33777539&hst_1 |archive-url=https://web.archive.org/web/20120927174941/http://infotrac.galegroup.com/itw/infomark/322/785/116929157w16/purl%3Drc1_TTDA_0_CS33777539%26dyn%3D17%21xrn_1_0_CS33777539%26hst_1 |archive-date=27 September 2012 |url-status=live |url-access=subscription}}</ref> and in August 1965, parliamentary powers were granted. Detailed planning took place, although public spending cuts led to postponement of the scheme in 1967 before [[Invitation to tender|tender]]s were invited.{{sfn|Connor|2001|p=99}}

With the Aldwych branch receiving no extensions, it remained a lightly used shuttle service from Holborn. The branch was considered for closure many times, but it survived.{{sfn|Connor|2001|pp=98–,99}} Saturday services were fully withdrawn on 5 August 1962, leaving the line with a peak hour only shuttle on weekdays.{{sfn|Horne|2007|p=134}} In 1993, The original 1907 lifts, which now failed to meet the safety standards at the time, required replacement at a cost of over £3&nbsp;million. As a result, in August 1993, a public inquiry was held for closure of the short branch line. On 30 September 1994, the branch was closed to traffic.{{refn|The [[Epping tube station|Epping]] to [[Ongar railway station|Ongar]] section of the [[Central line (London Underground)|Central line]] also closed on 30 September.{{sfn|Rose|1999}}|name=note4|group=note}} The disused station is now used for commercial filming and as a training facility, with the line retaining its link to the rest of the Piccadilly line.{{sfn|Horne|2007|pp=134–135}}

===Notable incidents and events===
====King's Cross fire====
{{main article|King's Cross fire}}

[[File:Memorial plaque with clock, King's Cross St. Pancras tube station, London.jpg|thumb|Memorial plaque of the [[King's Cross fire]] erected at the station]]

On 18 November 1987, the large [[King's Cross fire]] broke out, the incident being near the Northern/Piccadilly line escalators which killed 31 people.{{sfn|Horne|2007|p=132}}{{sfn|Day|Reed|2010|p=191}} As a result, wooden escalators were replaced at all Underground stations.<ref>{{cite hansard | house = House of Commons | url = https://api.parliament.uk/historic-hansard/commons/1989/apr/12/kings-cross-fire-fennell-report#S6CV0150P0_19890412_HOC_145 | title = King's Cross Fire (Fennell Report) | date = 12 April 1989 | column_start = 915 | column_end = 917 | speaker = [[Paul Channon]] | access-date = 17 August 2020 | archive-url = https://web.archive.org/web/20121227101227/http://hansard.millbanksystems.com/commons/1989/apr/12/kings-cross-fire-fennell-report#S6CV0150P0_19890412_HOC_145 | archive-date = 27 December 2012 | url-status = live }}</ref><ref>{{cite news |url= https://www.telegraph.co.uk/news/obituaries/law-obituaries/8618848/Sir-Desmond-Fennell.html |work=The Daily Telegraph |location= London |title=Sir Desmond Fennell |date=5 July 2011 |access-date=17 August 2020 |archive-url= https://web.archive.org/web/20180613050755/https://www.telegraph.co.uk/news/obituaries/law-obituaries/8618848/Sir-Desmond-Fennell.html |archive-date=13 June 2018 |url-status=live }}</ref>{{refn|All except the two at [[Greenford station]] were replaced. These have since been decommissioned on 20 March 2014,<ref>{{cite news|url=http://www.london24.com/news/transport/tube_s_only_wooden_escalator_to_carry_last_passengers_1_3419976 |title=Tube's only wooden escalator to carry last passengers |last=Mann |first=Sebastian |date=11 March 2014 |publisher=London 24 |access-date=17 August 2020 |url-status=dead |archive-url=https://web.archive.org/web/20141029143253/http://www.london24.com/news/transport/tube_s_only_wooden_escalator_to_carry_last_passengers_1_3419976 |archive-date=29 October 2014 }}</ref><ref>Fact 121 in the reference. {{cite news |url= https://www.telegraph.co.uk/travel/destinations/europe/united-kingdom/england/london/articles/London-Underground-150-fascinating-Tube-facts/ |title=London Underground: 150 Fascinating Tube Facts |last=Attwooll |first=Jolyon |date=9 January 2017 |access-date=17 August 2020 |url-status=live |work=The Telegraph |location= London |archive-url= https://web.archive.org/web/20200817173309/https://www.telegraph.co.uk/travel/destinations/europe/united-kingdom/england/london/articles/London-Underground-150-fascinating-Tube-facts/ |archive-date=17 August 2020}}</ref> being replaced with an [[Inclined elevator|inclined lift]] and an up metal escalator the following year.<ref>{{cite press release |url=https://tfl.gov.uk/info-for/media/press-releases/2015/october/uk-first-as-incline-lift-opens-at-greenford-tube-station |title=Incline lift at Greenford Tube Station is UK First |publisher=[[Transport for London]] |date=20 October 2015 |access-date=17 August 2020 |url-status=live |archive-url= https://web.archive.org/web/20200817181048/https://tfl.gov.uk/info-for/media/press-releases/2015/october/uk-first-as-incline-lift-opens-at-greenford-tube-station |archive-date=17 August 2020}}</ref>|group=note}} The Piccadilly line platforms remained open, but with the escalators to the ticket hall closed for repairs. Access was temporarily via the Victoria line or [[Kings Cross Midland City|Midland City platforms]]. New escalators were fully installed on 27 February 1989.{{sfn|Croome|Jackson|1993|pp=259,262}}

====7 July 2005 London bombings====
{{main article|7 July 2005 London bombings}}
On 7 July 2005, a Piccadilly line train was attacked by [[Suicide attack|suicide bomber]] [[Germaine Lindsay]] in the [[7 July 2005 London bombings|day's London bombings]].<ref>{{cite news |url=http://news.bbc.co.uk/2/hi/uk_news/politics/4689739.stm |title=Image of Bombers' Deadly Journey |publisher=[[BBC News]] |date=17 July 2005 |access-date=17 August 2020 |url-status=live |archive-url=https://web.archive.org/web/20200817152016/http://news.bbc.co.uk/2/hi/uk_news/politics/4689739.stm |archive-date=17 August 2020}}</ref> The blast occurred at 08:50 [[British Summer Time|BST]] while the train was between King's Cross St Pancras and Russell Square. It was part of a co-ordinated [[Islamic terrorism|Islamist terrorist attack]] on London's transport network, and was synchronised with three other attacks: two on the [[Circle line (London Underground)|Circle line]] and one on a bus at [[Tavistock Square]]. The Piccadilly line bomb led to the largest number of fatalities, with 26 people reported killed. Owing to it being a deep-level line, evacuation of station users and access for the emergency services proved difficult.<ref name="north-diary">{{cite news |url=http://news.bbc.co.uk/2/hi/uk_news/4670099.stm |title=Coming together as a city |access-date=17 August 2020 |date=15 July 2005 |last=North |first=Rachel |publisher=[[BBC News]] |url-status=live |archive-url=https://web.archive.org/web/20200817153435/http://news.bbc.co.uk/2/hi/uk_news/4670099.stm |archive-date=17 August 2020}}</ref> Shuttle services were introduced between Hyde Park Corner and the Heathrow loop, between Acton Town and Rayners Lane, and between Arnos Grove and Cockfosters. Full service was restored on 4 August, four weeks after the bombing.{{sfn|Horne|2007|p=132}}<ref name=culgpiccadilly />

====100-year celebration====
On 15 December 2006, a 100-year celebration of the Piccadilly line was launched. A birthday card was revealed by [[Tim O'Toole (businessman)|Tim O'Toole]], then London Underground Managing Director at [[Leicester Square tube station|Leicester Square station]].{{sfn|Horne|2007|p=140}}

==Architecture==
{{multiple image
| align        = center
| direction    = horizontal
| header       = A variety of architecture on '''Piccadilly line''' stations
| header_align = center
| image1       = Russell Square station.jpg
| width1       = {{#expr: (150 * 1600/ 1200) round 0}}
| alt1         = Ox-blood [[terracotta]] with semicircular windows on first floor
| caption1     = [[Russell Square tube station|Russell Square]], by [[Leslie Green]]
| image2       = Sudbury Town stn main entrance.JPG
| width2       = {{#expr: (150 * 1600/ 1200) round 0}}
| alt2         = A red brick rectangular box shaped building with a [[concrete]] roof and two pairs of [[Glazing (window)|glazed]] screens
| caption2     = [[Sudbury Town tube station|Sudbury Town]], the exemplar station
| image3       = Southgate station building.JPG
| width3       = {{#expr: (150 * 1600/ 1200) round 0}}
| alt3         = A low circular building with a wide awning is surmounted by a glazed column with a metal ball on the top
| caption3     = [[Southgate tube station|Southgate]]'s unique roof by [[Charles Holden|Holden]]
| image4       = Arnos tube interior.jpg
| width4       = {{#expr: (150 * 1600/ 1200) round 0}}
| alt4         = Passimeter in a station ticket hall
| caption4     = [[Arnos Grove tube station|Arnos Grove]] with passimeter
}}
Most of the deep level stations opened in the first phase between Finsbury Park and Hammersmith were built to a design by [[Leslie Green]].{{sfn|Wolmar|2005|p=175}} This consisted of two-storey [[Steel frame|steel-framed]] buildings faced with dark oxblood red [[Glaze (metallurgy)|glazed]] [[terracotta]] blocks, with wide semi-circular windows on the upper floor. Earl's Court and Barons Court stations was built with a red brick building by Harry Wharton Ford,{{sfn|Wallinger|Self|Warner|Wolmar|2014|pp=155,277}} with semicircular windows on the second level and embedded names of the railways which operated through the station. Both station buildings are Grade II listed,<ref name="eh_1358162">{{NHLE|num=1358162|desc=Earl's Court Station |access-date=18 August 2020}}</ref><ref name="EH 1358562">{{National Heritage List for England| num=1358562| desc=Barons Court Underground Station |access-date=1 November 2020}}</ref> and this building design at the former replaced a wooden hut building.{{sfn|Day|Reed|2010|p=24}}{{sfn|Martin|2012|p=79}}

Extensions of the Piccadilly line towards the west and north in the 1930s had new stations designed by [[Charles Holden]] of Adams, Holden & Pearson architectural practice. These designs were inspired by modern architecture seen in a 1930 trip to several European Countries.{{sfn|Horne|2007|p=61}}<ref>{{cite web |title=Underground Journeys: Changing the face of London Underground |url=http://www.architecture.com/LibraryDrawingsAndPhotographs/Exhibitionsandloans/VARIBAArchitecturePartnershipexhibitions/UndergroundJourneys/ChangingthefaceofLondonUnderground/ChangingTheFaceOfLondonUnderground.aspx |publisher=[[Royal Institute of British Architects]] |access-date=19 February 2011 |url-status = dead|archive-url=https://web.archive.org/web/20110504024645/http://www.architecture.com/LibraryDrawingsAndPhotographs/Exhibitionsandloans/VARIBAArchitecturePartnershipexhibitions/UndergroundJourneys/ChangingthefaceofLondonUnderground/ChangingTheFaceOfLondonUnderground.aspx |archive-date=4 May 2011 }}</ref>

Several stations on the western extension originally built by the District Railway were reconstructed. The new designs used brick, concrete and glass to construct simple geometrical shapes, such as cylinders and rectangles. The first prototype station was [[Sudbury Town tube station|Sudbury Town station]], which has a brick cuboid box topped with a concrete slab roof for the main structure, with tall windows above the entrances. This design was replicated across many other stations.{{sfn|Cherry|Pevsner|1991|p=140}} Due to the workload, some stations' designs were carried out as collaborations with the Underground's own Architect, [[Stanley Heaps]] (Boston Manor, Osterley, Ealing Common and Hounslow West), or architects from other practices ([[Reginald Uren]] for Rayner's Lane) or entirely by another practice in Holden's style (Felix Lander for Park Royal).{{sfn|Powers|2007}}{{sfn|Day|Reed|2008|p=114}} The new stations built for the northern extension were also part of the design schemes undertaken by Holden. Southgate was distinctively different, with a round base carrying a cylindrical panel of [[clerestory]] windows, topped by an illuminated feature with a bronze ball.{{sfn|Day|Reed|2008|p=103}} The ticket halls had passimeters, which functioned as free-standing ticket booths. Most of them ceased to be used when automatic ticket gates were introduced, although some have been converted for retail use.{{sfn|Horne|2007|pp=82,131}} Many of these Holden-designed stations are [[listed building]]s, Oakwood, Southgate, and Arnos Grove being among the early receivers in 1971.{{sfn|Horne|2007|p=82}}<ref name="eh_1358981">{{NHLE|num=1358981 |desc=Arnos Grove Underground Station |access-date=18 August 2020 }}</ref><ref name="eh_1188692">{{NHLE | num=1188692 | desc=Southgate Underground Station | access-date=18 August 2020 }}</ref><ref name="eh_1078930">{{NHLE |num=1078930 |desc=Oakwood Underground Station |access-date=18 August 2020}}</ref>

Stations in Central London were modernised. Green Park received a new shelter at the southern entrance; Piccadilly Circus had its ticket hall moved below street level. Both of these changes were designed by Holden,{{sfn|Karol|2007|pp=481–484}} with the latter's station ticket hall having artwork commemorating Frank Pick added in 2016.<ref>{{Cite web|title=Train of thought: artists Langlands & Bell celebrate Frank Pick's design philosophy|url=https://www.wallpaper.com/art/langlands-bell-celebrate-frank-pick-design-philosophy-at-piccadilly-circus|last=Magazine|first=Wallpaper*|date=7 November 2016 |website=Wallpaper*|access-date=18 August 2020 |url-status=live |archive-url=https://web.archive.org/web/20200818170637/https://www.wallpaper.com/art/langlands-bell-celebrate-frank-pick-design-philosophy-at-piccadilly-circus |archive-date=18 August 2020}}</ref><ref>{{Cite web|title=Beauty < Immortality|url=https://art.tfl.gov.uk/projects/beauty-immortality/|website=Art on the Underground|language=en |access-date=18 August 2020 |url-status=live |archive-url=https://web.archive.org/web/20200818170339/https://art.tfl.gov.uk/projects/beauty-immortality/ |archive-date=18 August 2020}}</ref> Green Park also was built with a new entrance at a corner of Devonshire House, which has Portland Stone clad steel frames.{{sfn|Connor|2006|p=106}} It features [[Greco-Roman world|Graeco-Roman]] details, and is Grade II listed.<ref name="eh_1226746">{{English Heritage List entry |num=1226746 |desc=Devonshire House |access-date=18 August 2020}}</ref> Some stations kept their original buildings. [[South Ealing tube station|South Ealing]], where a temporary wooden station ticket hall was constructed when the line was quadrupled, was an anomaly; a modern station was not provided until the 1980s.{{sfn|Horne|2007|p=55}}{{sfn|Wallinger|Self|Warner|Wolmar|2014|p=287}}{{refn|Sources differ by year. Horne's mentioned 1989, while Wallingers' mentioned 1983.|group=note}}

Green's stations such as [[Caledonian Road tube station|Caledonian Road]] have bands of tiles arching overhead on the curved platform ceilings and above the tracks spaced {{convert|11–12|ft|m|abbr=on}} apart. Along the platform walls, geometrical patterns of tiles were arranged in a horizontal band; varying among stations. Arc lighting was complemented with incandescent lamps to illuminate the platforms. Signage decorations, also designed by Green, present spelt out the station name in letters {{convert|15|in|cm|abbr=on}} high.{{sfn|Horne|2007|p=22}}<ref name="eh_1401086">{{National Heritage List for England |num=1401086 |desc=Caledonian Road Underground Station |access-date=18 August 2020}}</ref>{{sfn|Wolmar|2005|p=175}}{{refn|This decoration concept was tested and worked on Bakerloo line stations, showing uniform style yet giving each station a unique appearance.{{sfn|Horne|2007|p=22}}|group=note}} Stations on the northern extension had particular biscuit (square) tiles on platform walls, with different [[frieze]] colours at each station. A few stations like Southgate and Bounds Green have [[art deco]] uplighters on escalators and the lower landings.<ref name="eh_1188692"/><ref name="eh_1393641">{{National Heritage List for England |num=1393641 |desc=Bounds Green Underground Station (Including No. 38) |access-date=3 April 2015}}</ref> [[Floodlighting]] was used considerably to provide a spacious ambience. [[Ventilation duct]]s were by the platforms walls, sealed with bronze art deco style [[Grille (architecture)|grille]]s.{{sfn|Horne|2007|pp=86–87}} Oakwood was built with a concrete canopy, with roof lights and cylindrical light fittings designed by Heaps.<ref name="eh_1078930"/>

==Infrastructure==

===Signalling and electricity===
[[File:Lots.road.power.station.london.arp.jpg|thumb|[[Lots Road Power Station]], disused and planned to be redeveloped]]
The line from Cockfosters to Heathrow and South Harrow is controlled from a control centre at [[South Kensington tube station|South Kensington]],<ref name=isgaz1950signalpicc>{{cite news |url= https://www.islingtongazette.co.uk/news/piccadilly-line-trains-still-run-by-obsolete-signalling-system-from-the-1950s-1-5517895 |title=Piccadilly line trains still run by obsolete signalling system from the 1950s |work=Islington Gazette |date=15 May 2018 |last=Gelder |first=Sam |access-date=31 August 2020 |url-status=live |archive-date=31 August 2020 |archive-url= https://web.archive.org/web/20200831074109/https://www.islingtongazette.co.uk/news/piccadilly-line-trains-still-run-by-obsolete-signalling-system-from-the-1950s-1-5517895}}</ref> which replaced the old Earl's Court control centre, which was shared with the District line.<ref>{{cite web |last=Signalman |first=Llangollen |url= https://www.flickr.com/photos/llangollen_signalman/albums/72157637392832414 |title=Earls Court Control Room |publisher=Flickr |date=6 November 2013 |access-date=14 July 2017}}</ref> Rayners Lane signal cabin is responsible for signalling the Piccadilly line from just northwest of South Harrow to Uxbridge, as well as the Metropolitan line joining at Rayners Lane.<ref>{{cite web|last=Signalman |first=Llangollen |url=https://www.flickr.com/photos/llangollen_signalman/albums/72157657032080114 |title=Rayners Lane |publisher=Flickr |date=1 October 2015 |access-date=14 July 2017}}</ref> The signalling system is expected to be upgraded in line with the Deep Tube upgrade, which will increase line frequencies up to 33 tph.<ref name=isgaz1950signalpicc/> Trains may also be able to make a permanent additional stop at Turnham Green following this upgrade.<ref>{{cite news |url= https://www.guardian-series.co.uk/news/18213985.tfl-says-piccadilly-tube-upgrade-number-one-priority/ |title=TfL says Piccadilly Tube upgrade is "number one priority" |date=6 February 2020 |access-date=31 August 2020 |last=Mathewson |first=Jessie |work=East London & West Essex Guardian |url-status=live |archive-date=31 August 2020 |archive-url= https://web.archive.org/web/20200831075525/https://www.guardian-series.co.uk/news/18213985.tfl-says-piccadilly-tube-upgrade-number-one-priority/ }}</ref>

When the line was opened from Finsbury Park to Hammersmith, its [[signalling]] system was identical to the Bakerloo and District lines. Small cabins at each location of crossover installed controlled the signals there. Single lamps displayed track clearance in the form of green or red, with variations of yellow at difficult-to-spot locations. This equipment was supplied by [[Westinghouse Rail Systems|Westinghouse]] and operated using compressed air. The exception was between West Kensington and Hammersmith, where it was controlled by District Railway signal boxes, and had semaphore signals instead.{{sfn|Horne|2007|p=27}}{{sfn|Horne|2006|pp=37–40}} The Piccadilly line extensions resulted in resignalling on tracks west of Barons Court. Signal cabins were adjusted and new ones were added at Hammersmith, Acton Town and Northfields. A mixture of [[Railway semaphore signal|semaphore]] and colour-light signals were used on the four-track section. Signalling was redone on the new Uxbridge branch.{{sfn|Horne|2007|p=57}}{{refn|Most of the existing semaphore signals on the District line branch to South Harrow were replaced with coloured light signals between October and December 1932.{{sfn|Horne|2007|p=57}}|group=note}}

Speed control was introduced at several stations to enhance the signalling system after World War II. This enabled a train to proceed slowly into an occupied platform without stopping in front of another before it departed, thus improving headways. The last semaphore signal, at [[Ealing Common tube station|Ealing Common]], was replaced in November 1953.{{sfn|Horne|2007|p=128}} A control room was built at Earl's Court to centralise supervision of most of the line signalling in the 1960s, while Rayners Lane signal cabin was, and still is, the main control centre of the Rayners Lane to Uxbridge portion;{{sfn|Horne|2007|p=126}} shared with the Metropolitan line.<ref name=cartomap /> 1930s automatic signalling equipment was updated in the 1970s and 1980s.{{sfn|Horne|2007|p=127}}

The UERL built a large power station that would be capable of providing power for the District line and the underground lines planned. Work began in 1902 at Lots Road, by [[Counter's Creek|Chelsea Creek]], and in February 1905 Lots Road Power Station began generating electricity at {{nowrap|{{val|11|u=kV}} {{Fraction|33|1|3}} Hz}}, conveyed by high-voltage cables to substations that converted this to approximately {{val|550|u=V|s=&nbsp;DC}}.{{sfn|Horne|2006|p=40}} On the Piccadilly line, electricity was transmitted via underground ducts to Earl's Court, which was then distributed to different substations.{{sfn|Horne|2007|p=27}}{{refn|Direct traction current was also provided from District line substations at Earl's Court and South Kensington.{{sfn|Horne|2007|p=27}}|group=note}} Power supply for the Cockfosters extension was initially generated by the North Metropolitan Electric Power Supply Company at Wood Green.{{sfn|Horne|2007|pp=78–81}} It was later supplied by Lots Road station. The [[National Grid (Great Britain)|National Grid network]] took over the supply on the Ravenscourt Park to Uxbridge and Northfields section. Lots Road was permanently closed on 31 October 2003, being also replaced by power supply from the National Grid Network. Emergency lighting, powered by batteries, is available at every station, with emergency supply from a support power station in [[Greenwich]].{{sfn|Horne|2007|p=127}}

===Depots and sidings===
[[File:Northfields Depot (18036366511).jpg|thumb|Northfields Depot, with an [[London Underground S7 and S8 Stock|S stock]] train]]
The line has two depots, at [[Cockfosters tube station|Cockfosters]] and [[Northfields Depot|Northfields]]. The former site is near [[Trent Park]], and was the preferred site over [[Oakwood tube station|Oakwood]], which was smaller,{{sfn|Horne|2007|p=66}} and its only access point was south of the station. Subsequently, Oakwood was built with an island platform, with its intended three-track terminus layout moved to Cockfosters.{{sfn|Horne|2007|p=72}} Light maintenance and cleaning of trains is done here, with the latter site, being the main depot, having train maintenance facilities.{{sfn|Horne|2007|p=127}} Northfields depot is also double-ended, with access from just west of [[Boston Manor tube station|Boston Manor station]]{{sfn|Horne|2007|p=50}} and Northfields station. For it to be built, the latter station had to be rebuilt nearer to [[South Ealing tube station|South Ealing station]].{{sfn|Horne|2007|p=55}} The depot was opened earlier than the Hounslow extension, on 4 July 1932, and fully electrified two months later.{{sfn|Horne|2007|p=57}}<ref name=cartomap/>{{refn|When opened, some District line trains were stabled here.{{sfn|Horne|2007|p=57}}|group=note}}

Single [[Siding (rail)|sidings]] are placed at Rayners Lane, Oakwood, Down Street (Hyde Park Corner), and Wood Green. Arnos Grove, Acton Town, South Harrow, Uxbridge, Hammersmith and Heathrow Terminal 5 have more than one siding for reversing trains or storing them.<ref name=cartomap/> Four [[Crossover (rail)|crossovers]] were built for the initial line opening in 1906,{{sfn|Horne|2007|p=27}} [[Hounslow Central tube station|Hounslow Central]] on 3 March 1923,{{sfn|Horne|2007|p=46}} and double crossovers at South Harrow were added in the 1930s.{{sfn|Horne|2007|p=57}}

Crossovers with other lines are present on the Piccadilly line. A connecting tunnel from the northbound Piccadilly line at King's Cross St Pancras to the northbound [[Northern line]] Bank branch was constructed in 1927.{{sfn|Horne|2007|p=98}}{{refn|It was built to facilitate rolling stock transfers between lines and to reach [[Acton depot|Acton works]].{{sfn|Horne|2007|p=98}}|group=note}} At Finsbury Park, a set of crossovers in the south were retained where trains can cross over onto the Victoria line.{{sfn|Horne|2007|p=114}}

[[Lillie Bridge Depot|Lillie Bridge]] was the main depot when the Piccadilly line was initially opened. Trains entering service on the line had to reverse and enter the District line tracks first via [[West Kensington tube station|West Kensington]].{{sfn|Horne|2007|p=26}}{{sfn|Follenfant|1974|p=130}} When the Piccadilly and District line tracks were realigned in the 1930s, access points into the depot had to be altered.{{sfn|Horne|2007|p=54}}{{sfn|Follenfant|1974|p=131}} When the line was extended to Northfields and Cockfosters in 1933, all trains except seven{{refn|This figure excluded trains serving the Aldwych branch which were also parked at the depot.{{sfn|Horne|2007|p=57}}|group=note}} were stabled at the newer depot.{{sfn|Horne|2007|p=57}} Once the Cockfosters depot was opened, Lillie Bridge was converted to a maintenance depot, where it housed only engineers' and materials trains.{{sfn|Horne|2007|p=90}}{{sfn|Follenfant|1974|p=130}}

===Station lifts and escalators===
Most original deep-level stations were installed with lifts and stairs, with some descending directly down to platform level.{{sfn|Wolmar|2005|p=188}} Many of these were given an overhaul in the 1930s with escalators replacing lifts for quicker passenger flow.{{sfn|Badsey-Ellis|2016|p=212}}{{sfn|Horne|2007|p=93}} Underground stations on the Cockfosters extension were built with access mainly via escalators; each station shaft are able to fit three escalators, but some stations had two escalators with a stairwell by the middle. Escalators at Bounds Green, Wood Green and Manor House travel at {{convert|165|ft|m}} per minute, which were then the quickest on the network.{{sfn|Horne|2007|p=82}} All of the original lifts were either replaced by new equipment or were converted to escalators. [[Alperton tube station|Alperton]] was the only above ground station to have an escalator, which was transferred over from the [[Festival of Britain]], but was decommissioned in 1988.{{sfn|Horne|2007|p=128}} Stations such as Green Park and King's Cross St Pancras were installed with new lifts to provide step-free access to every platform by the [[2012 Summer Olympics]].<ref name="upgrade2008">{{cite press release |url=https://tfl.gov.uk/info-for/media/press-releases/2008/august/green-park-tube-station-to-be-upgraded-ahead-of-london-2012-games |title=Green Park Tube station to be upgraded ahead of London 2012 Games |publisher=[[Transport for London]] |date=18 August 2008 |access-date=30 August 2020 |url-status=live |archive-date=30 August 2020 |archive-url=https://web.archive.org/web/20200830162224/https://tfl.gov.uk/info-for/media/press-releases/2008/august/green-park-tube-station-to-be-upgraded-ahead-of-london-2012-games }}</ref><ref name="upgrade2011">{{cite press release |url=https://tfl.gov.uk/info-for/media/press-releases/2011/september/transformation-of-green-park-station-nears-completion |title=Transformation of Green Park station nears completion |publisher=[[Transport for London]] |date=6 September 2011 |access-date=30 August 2020 |url-status=live |archive-date=30 August 2020 |archive-url=https://web.archive.org/web/20200830162224/https://tfl.gov.uk/info-for/media/press-releases/2008/august/green-park-tube-station-to-be-upgraded-ahead-of-london-2012-games}}</ref><ref>{{Cite magazine |last=Cole |first=Margo |date=22 April 2010 |title=Major Project – King's Cross Underground Ticket Halls |url=http://leewoodprojects.co.uk/wp-content/uploads/2010/07/kings-cross-st-pancras-nce1.pdf |archive-url=https://web.archive.org/web/20170102152229/http://leewoodprojects.co.uk/wp-content/uploads/2010/07/kings-cross-st-pancras-nce1.pdf |archive-date=2017-01-02 |url-status=live |magazine=New Civil Engineer |pages=27–29 }}</ref><ref>{{cite press release |url=https://tfl.gov.uk/info-for/media/press-releases/2010/september/kings-cross-st-pancras-tube-station-is-stepfree-with-10-new-lifts |title=King's Cross St. Pancras Tube station is step-free with 10 new lifts |date=27 September 2010 |website=tfl.gov.uk |publisher=Transport for London|access-date=30 August 2020 |url-status=live |archive-date=30 August 2020 |archive-url=https://web.archive.org/web/20200830162625/https://tfl.gov.uk/info-for/media/press-releases/2010/september/kings-cross-st-pancras-tube-station-is-stepfree-with-10-new-lifts}}</ref>

==Services==
[[File:UXBRIDGE-05 120512 CPS (7160089779).jpg|thumb|A Metropolitan line train at Uxbridge, with a Piccadilly line train to the left. This section is shared between the two lines.]]
Journey times on the Piccadilly line are usually around an hour and a half. Train [[Dwell time (transportation)|dwell times]] are slightly longer at some stations, such as at Heathrow Terminals 4 and 5 stations. The former requires 8 minutes, while the latter needs 7 minutes to coordinate with the alternate Heathrow service schedule. The busiest section, as of 2016, is between King's Cross St Pancras and Russell Square. This is expected to expand, between Holloway Road and Holborn in the 2040s.<ref>{{cite web |url=http://content.tfl.gov.uk/travel-in-london-report-12.pdf |title=Travel in London Report |edition=12th |publisher=[[Transport for London]] |date=2019 |access-date=3 September 2020 |pages=248–250 |url-status=live |archive-date=12 August 2020 |archive-url=https://web.archive.org/web/20200812151641/http://content.tfl.gov.uk/travel-in-london-report-12.pdf}}</ref><ref>{{cite web |url=https://www.london.gov.uk/sites/default/files/strategic_transport_modelling_report.pdf |title=Strategic Transport Modelling Report |date=December 2017 |pages=21–22 |access-date=3 September 2020 |publisher=[[Transport for London]] |url-status=live |archive-date=3 September 2020 |archive-url=https://web.archive.org/web/20200903163740/https://www.london.gov.uk/sites/default/files/strategic_transport_modelling_report.pdf}}</ref> The central section between Earl's Court and King's Cross St Pancras is in [[List of stations in London fare zone 1|Fare Zone 1]], to Manor House and Turnham Green in [[List of stations in London fare zone 2|Zone 2]], and to Bounds Green, Park Royal and Northfields in [[List of stations in London fare zone 3|Zone 3]]; to Southgate, Sudbury Hill and Hounslow Central in [[List of stations in London fare zone 4|Zone 4]], to Cockfosters, Hatton Cross and Eastcote in [[List of stations in London fare zone 5|Zone 5]], and to Uxbridge and Heathrow Terminals in [[List of stations in London fare zone 6|Zone 6]].<ref name=tubemap/> 79 trains are required to operate a 24 trains per hour (tph) peak-hour service on the line,<ref name=piccfactstfl/> while typical off-peak services are generally as follows (as of 6 July 2020):<ref name=culgpiccadilly /><ref name=luwttpicc2020>{{cite web |title=London Underground Working Timetable – Piccadilly line |url=http://content.tfl.gov.uk/ttn-222-20-picc.pdf |publisher=[[Transport for London]] |date=6 July 2020 |url-status =live |access-date=4 September 2020 |archive-url=https://web.archive.org/web/20200829184246/http://content.tfl.gov.uk/ttn-222-20-picc.pdf |archive-date=29 August 2020}}</ref>

* 6 tph Cockfosters – Heathrow Terminal 4
* 6 tph Cockfosters – Heathrow Terminal 5
* 3 tph Cockfosters – Rayners Lane
* 3 tph Cockfosters – Uxbridge
* 3 tph Arnos Grove – Northfields

Trains also make an additional stop at {{stl|London Underground|Turnham Green}} in the early mornings and late evenings.<ref name=luwttpicc2020 /> Night Tube services have operated every 10 minutes between Cockfosters and Heathrow Terminal 5 since 16 December 2016. No Night Tube services operate to Heathrow Terminal 4 or Uxbridge.<ref>{{cite web |url=https://tfl.gov.uk/campaign/tube-improvements/what-we-are-doing/night-tube |title=The Night Tube |publisher=[[Transport for London]] |access-date=21 August 2020 |url-status=live |archive-url=https://web.archive.org/web/20200821161701/https://tfl.gov.uk/campaign/tube-improvements/what-we-are-doing/night-tube |archive-date=21 August 2020}}</ref><ref name=culgpiccadilly />

===Historical services===
On 11 October 1909, peak-hour services were altered to have trains skipping certain stops to improve journey times. Trains were marked with "Non Stop", which were deemed unpopular and ambiguous among passengers. Illuminated signs were added on platforms in 1932 to address this issue. Pairs of stations were the norm, such as Holloway Road and York Road, and Caledonian Road and [[Arsenal tube station|Gillespie Road]]. After World War I, [[Covent Garden tube station|Covent Garden]], Russell Square, South Kensington, Brompton Road and Gloucester Road were among the stations skipped. [[Boston Manor tube station|Boston Manor]], South Ealing, North Ealing and Barons Court were included into these patterns by 1938. Skip-stop services were discontinued in June 1947.{{sfn|Horne|2007|pp=32,75,93}}

In 1930, during the planning of the northward and westward extensions, a 30tph peak-hour service was proposed between Wood Green and Turnham Green. This was preferred over an alternate skip-stop service through [[Bounds Green tube station|Bounds Green]].{{sfn|Horne|2007|p=75}}{{refn|Several stations were planned to be closed to improve running times, and Bounds Green would not have been included as a station.{{sfn|Horne|2007|p=75}}|group=note}} When the Piccadilly line was initially extended to Northfields in 1933, [[South Ealing tube station|South Ealing]] was skipped. It was eventually served on 29 April 1935 by off-peak trains, and peak services in May 1942.{{sfn|Horne|2007|p=59}}

When the Piccadilly line shared its storage of trains with the District line at [[Lillie Bridge Depot]],{{sfn|Horne|2007|p=26}} some trains started and ended their service at [[West Kensington tube station|West Kensington]]; a few of these ran empty between West Kensington and Hammersmith. These services ceased on 27 October 1991.{{sfn|Horne|2007|p=128}}

During disruptions, Piccadilly line trains were able to run on the “local” District line tracks, stopping at all stations between Acton Town and Hammersmith. The crossover points at Hammersmith were decommissioned and subsequently removed in the early-2020s meaning that this is no longer possible. <ref name="culgpiccadilly" />

==Rolling stock==
{{main|London Underground 1973 Stock}}
{{multiple image
| align             = right
| direction         = vertical
| width             = 230
| image1            = Northfields. (120).jpg
| alt1              = A westbound Piccadilly line train at Northfields, formed of a six-car 1973 stock.
| caption1          = 1973 stock at Northfields, July 2015
| image2            = Barons Court Station - geograph.org.uk - 1762897.jpg
| alt2              = A westbound Piccadilly line train at Barons Court station, operated by a seven-car 1959 stock.
| caption2          = 1959 Stock train at {{stl|London Underground|Barons Court}}
| image3            = 
| caption3          = 2024 Stock train rendering.
}}

The {{convert|107.2|m|ft|abbr=on|order=flip}} six-car [[London Underground 1973 Stock|1973 tube stocks]] provide services on the Piccadilly line, which were built between 1974 and 1977 by [[Metro-Cammell]]. These trains were built {{convert|6|ft|m|abbr=on}} longer than the 1959 stock trains to accommodate more luggage space{{sfn|Croome|Jackson|1993|pp=408–409}} and speed up journey times with more comfort. As of 2020, their livery is of standard London Underground corporate of blue, white and red. They were previously unpainted, exposing the aluminium [[alloy]] material.{{sfn|Horne|2007|p=122}} Traction [[voltage]] is at {{Val|630|u=V|s=&nbsp;DC}} current powered by the third and fourth rail.<ref name="wdtk-lu">{{cite web|last1=Neil|first1=Graham|title=London Underground Rolling Stock Information Sheet |date=4 August 2015 |edition=4th |url-status=live |archive-url=https://web.archive.org/web/20200826131852/https://www.whatdotheyknow.com/cy/request/284276/response/737827/attach/6/RS%20Info%20Sheets%204%20Edition.pdf |archive-date=26 August 2020 |url=https://www.whatdotheyknow.com/cy/request/284276/response/737827/attach/6/RS%20Info%20Sheets%204%20Edition.pdf |access-date=26 August 2020}}</ref> The first of these trains entered service on 18 August 1975.{{sfn|Horne|2007|p=123}}{{refn|One train was used during the Hatton Cross extension opening on 19 July that same year.{{sfn|Horne|2007|p=123}}|group=note}} They were refurbished by [[Bombardier Transportation|Bombardier]] from 1995 to 2000 in [[Wakefield, Yorkshire]].<ref>{{cite web |url= http://www.tfl.gov.uk/corporate/modesoftransport/londonunderground/rollingstock/1624.aspx |title=1973 |publisher= Transport for London |date=n.d. |access-date=20 April 2013| archive-url=https://web.archive.org/web/20130516015513/https://tfl.gov.uk/corporate/modesoftransport/londonunderground/rollingstock/1624.aspx| archive-date=16 May 2013}}</ref><ref>{{Cite press release |title=New Look Trains on the Piccadilly Line |url=http://www.londontransport.co.uk/press/picline.html |date=17 June 1996 |website=[[London Transport (brand)|London Transport]] |url-status=dead |archive-url=https://web.archive.org/web/19970111015700/http://www.londontransport.co.uk/press/picline.html |archive-date=11 January 1997 |access-date=27 August 2020}}</ref> Changes included the removal of transverse seating, [[strap hanger]]s replaced with [[grab bar]]s, new floor material and a full repaint into London Underground's corporate livery.<ref>{{cite web |url=https://www.squarewheels.org.uk/rly/stock/1973tubeStock/ |title=1973 tube stock |publisher=Squarewheels.org.uk |date=8 November 2010 |access-date=20 April 2013 }}</ref> A refurbished carriage on one train was first seen in service on 20 January 1991 to test the new interior concept.{{sfn|Horne|2007|p=135}}{{refn|The shared section between Rayners Lane and Uxbridge is also served by [[London Underground S7 and S8 Stock|S8 stock]] trains on the Metropolitan line.<ref>{{cite web |url= http://content.tfl.gov.uk/Part-1-Item05-Commissioners-Report-November-2012.pdf |title=Commissioner's Report |publisher=Transport for London |work=Board Meeting Documents |date=20 September 2012 |access-date=26 August 2020 |location=paragraph 3.2 |url-status=live |archive-url=https://web.archive.org/web/20200826151136/http://content.tfl.gov.uk/Part-1-Item05-Commissioners-Report-November-2012.pdf |archive-date=26 August 2020}}</ref> Between Hammersmith and Acton Town, it is parallel to the District line, which is served by S7 stock trains.<ref>{{cite news |last=Chandler |first=Mark |url= https://www.standard.co.uk/news/transport/catch-the-d-train-buffs-descend-on-tube-to-catch-last-ever-classic-d-stock-district-line-services-a3520901.html |title=Catch the D: Train buffs descend on Tube to catch last old-style D stock District line service |newspaper=London Evening Standard |date=21 April 2017 |access-date=26 August 2020 |url-status=live |archive-url= https://web.archive.org/web/20200826151511/https://www.standard.co.uk/news/transport/catch-the-d-train-buffs-descend-on-tube-to-catch-last-ever-classic-d-stock-district-line-services-a3520901.html |archive-date=26 August 2020}}</ref>|group=note}}

=== Future rolling stock ===
{{Main articles|London Underground 2024 Stock}}
In the late 1990s, the Labour government initiated a [[public–private partnership]] (PPP) to reverse years of underinvestment in [[London Underground]].<ref name=":422">{{Cite news |date=16 December 2000 |title=New blow to Tube sell-off plan |language=en-GB |work=[[BBC News]] |url=http://news.bbc.co.uk/2/hi/uk_news/politics/1072193.stm |access-date=7 March 2021}}</ref> [[Tube Lines]] planned to order 93 new Piccadilly line trains, which would enter service by 2014.<ref name=":13">{{Cite web |date=8 January 2003 |title=Details of Tube modernisation plans unveiled |url=http://www.tubelines.com/news/releases/200602/20030108.aspx |url-status=dead |archive-url=https://web.archive.org/web/20060519094016/http://www.tubelines.com/news/releases/200602/20030108.aspx |archive-date=19 May 2006 |access-date=8 March 2021 |website=Tube Lines}}</ref> In January 2007, Tube Lines started the process of ordering new Piccadilly line trains, by querying if train manufacturers would be interested in supplying them.<ref name=":16">{{Cite web |date=15 January 2007 |title=Tube Lines invites expressions of interest from manufacturers for new Piccadilly line trains |url=http://www.tubelines.com/news/releases/200701/20070115.aspx |url-status=dead |archive-url=https://web.archive.org/web/20090224092920/http://www.tubelines.com/news/releases/200701/20070115.aspx |archive-date=2009-02-24 |access-date=2022-06-16 |website=[[Tube Lines]]}}</ref> Contract award was anticipated for 2008, and trains would enter service on the Piccadilly line in 2014.<ref name=":16" /> However, TfL bought out the Tube Lines consortium after cost overruns in 2010, formally ending the PPP.<ref>{{cite news |date=8 May 2010 |title=Tube maintenance back 'in house' as new deal is signed |publisher=[[BBC]] |url=http://news.bbc.co.uk/1/hi/england/london/8669823.stm |accessdate=9 May 2010}}</ref>

In the mid 2010s, TfL began a process of ordering new rolling stock to replace trains on the Piccadilly, Central, Bakerloo and Waterloo & City lines.<ref name=":4">{{Cite web |date=October 2014 |title=New Tube for London - Feasibility Report |url=http://content.tfl.gov.uk/ntfl-feasibility-report.pdf |url-status=dead |archive-url=https://web.archive.org/web/20160305014932/http://content.tfl.gov.uk/ntfl-feasibility-report.pdf |archive-date=5 March 2016 |access-date=26 June 2022 |website=[[Transport for London]]}}</ref> A feasibility study into the new trains showed that new generation trains and re-signalling could increase capacity on the Piccadilly line by 60%, with 36 trains per hour.<ref name=":4" />

In June 2018, the [[Siemens Inspiro]] was selected.<ref>{{cite magazine |date=15 June 2018 |title=Siemens to supply London Underground deep tube fleet |url=http://www.metro-report.com/news/news-by-region/europe/single-view/view/siemens-to-supply-london-underground-deep-tube-fleet.html |magazine=Metro Report International}}</ref> These trains will have an open gangway design, wider doorways, air conditioning and the ability to run automatically with a new signalling system.<ref name=":14">{{Cite news |date=4 March 2021 |title=Piccadilly Line: Plans for new 'walk-through' trains unveiled |work=BBC News |url=https://www.bbc.com/news/uk-england-london-56273283 |access-date=5 March 2021}}</ref> However, TfL could only afford to order 94 trains at a cost of £1.5bn, and not the cost of resignalling and automating the line.<ref>{{Cite news |last=Harris |first=Simon |date=3 January 2018 |title=Plan to sell part of Tube fleet branded 'quite mad' |website=ITV News |url=https://www.itv.com/news/london/2018-01-03/plan-to-sell-part-of-london-underground-fleet-branded-quite-mad |access-date=6 March 2021}}</ref> Half of the trains will be built in [[Goole]], [[East Riding of Yorkshire]].<ref name=":10">{{cite news |date=15 June 2018 |title=East Yorkshire factory wins £1.5bn Tube train deal |publisher=BBC News |url=https://www.bbc.co.uk/news/uk-england-humber-44496526 |access-date=15 June 2018}}</ref> Trains are expected to enter service in 2025, and are currently undergoing testing at a depot in Germany.<ref name=":0">{{cite news |last=Lydall |first=Ross |date=4 March 2021 |title=First look: TfL unveils design of new Piccadilly line trains |work=Evening Standard |location=London |url=https://www.standard.co.uk/news/transport/design-new-piccadilly-line-trains-unveiled-tfl-b922086.html |access-date=4 March 2021}}</ref><ref>{{cite web | url=https://www.railwaygazette.com/metros/london-undergrounds-piccadilly-line-train-on-test/65383.article#:~:text=UK%3A%20The%20first%20of%2094,Test%20%26%20Validation%20Centre%20in%20Germany | title=London Underground's Piccadilly Line train on test }}</ref>

===Historical tube stocks===

The line was previously worked by the [[London Underground 1906 Stock|1906 gate stock]], which were manufactured in France and Hungary.{{sfn|Wolmar|2005|p=188}} The {{convert|52|ft|m|abbr=on}} carriages were connected to form three, four or five-car trains, and were designed to have a maximum of six cars per train. Built with steel as its main material, the interiors were covered by fireproof mahogany [[Wood veneer|veneer]].{{sfn|Horne|2007|p=28}} Six-car trains were implemented in 1917. Additional cars were ordered and brought into service between 1920 and 1921 to combat shortage of capacity.{{sfn|Horne|2007|p=34}} In late 1920s, plans were developed to replace these outdated stocks. Metropolitan Carriage, Wagon & Finance Company (Metro-Cammell's predecessor) was to build [[London Underground Standard Stock|standard tube stocks]], which were delivered within 1928 and 1929. Another batch of these were constructed in [[Feltham]] by the Union Construction company. All the gate stocks were decommissioned in June 1929.{{sfn|Horne|2007|p=35}} The new standard tube stocks have some wider doors on trailer cars and extra doors on the motor car. All doors are now air-operated.{{sfn|Bruce|1988|pp=63–64}}{{refn|The 1906 gate stock was still in use on the Aldwych shuttle.{{sfn|Horne|2007|p=36}}|group=note}} In 1929, it was suggested that a new prototype of tube stock should include three double doors on each side. These seven-car trains, also standard tube stocks, had carriages at least one foot longer. They were made to be lighter, and had better interior lighting. These new trains were completed in two periods, 1931 and 1934, which costed £1.20&nbsp;million in total.{{sfn|Bruce|1988|pp=67–69}}{{sfn|Horne|2007|pp=98–99}}

Due to ridership increasing by {{nowrap|61 per cent}} on the Uxbridge branch between 1931 and 1938, Piccadilly line trains were packed with passengers. New experimental trains were brought into service in 1936, which were formed of four or six cars. These trains had their control equipment (of seven different types from four different manufacturers) placed under the car floor, which enabled more space for passengers on both motor cars. While boarding times were decreased, some of the designs of control equipment were said to be less reliable than others. Nevertheless, they were a prototype for the design of the [[London Underground 1938 Stock|1938 stock]].{{sfn|Horne|2007|p=101}}{{sfn|Hardy|2001|p=62}} As a safety measure for World War II, trains initially had their lights switched off at night. It was later amended to illuminate trains with dim blue lamps, and then, largely enclosed reading lamps.{{sfn|Horne|2007|p=104}} Patronage on the line increased greatly after the war, which meant additional trains were needed. New 1938 stocks, together with the experimental trains were rebuilt to form a fleet of seven-car [[London Underground 1949 Stock|1949 stock]] trains, in operation from 1952.{{sfn|Horne|2007|p=107}}{{sfn|Croome|Jackson|1993|pp=313–314}}{{refn|Meanwhile, 1906 stock trains were withdrawn on the Aldwych branch in December 1956, being replaced by two experimental trains. One train was transferred to the [[Epping Ongar Railway|Epping — Ongar shuttle]] in 1957.{{sfn|Horne|2007|p=108}}|group=note}}

New test trains were manufactured again in the 1950s. Three prototype trains, branded as the [[1956 tube stock|1956 stock]], were trialled on the Piccadilly line in 1957 and 1958. These new trains would replace most of the Standard stock. It was successful, and 76 seven-car trains were placed on order as the [[London Underground 1959 Stock|1959 stock]].{{sfn|Croome|Jackson|1993|p=318}} These were built by Metro-Cammell, with the first train entering service on 14 December 1959.{{sfn|Horne|2007|p=110}}{{sfn|Bruce|1988|pp=87–88}}{{refn|The Central line had problems with the wearing old standard stock, which were in urgent need of replacement. Combined with electrification of [[British Rail]] lines which forecasted new journeys on the line, priority was given to use some of the 1959 stock before the 1962 stock was produced. Once the latter stocks were fully in service in May 1964, the 57 trains were transferred back onto the Piccadilly line.{{sfn|Croome|Jackson|1993|p=320}} Previously, the line already had 19 1959 stock trains in service. A three-car 1962 stock train was brought into service on the Aldwych shuttle to replace the experimental train.{{sfn|Horne|2007|pp=110–111}}|group=note}} The standard stocks were withdrawn by 1964,{{sfn|Croome|Jackson|1993|p=320}} and the 1938 stocks were slowly taken out of service due to age. The 1959 stocks were gradually transferred to the [[Northern line]] between November 1975 and October 1979, being replaced by the 1973 stock trains; the last of the latter coming into service on 5 October 1979.{{sfn|Horne|2007|p=123}}

A few 1938 trains were preserved, and in June 2011, one of these trains made a few shuttle trips on the line as part of an event in conjunction with Father's Day.<ref>{{cite news |url=https://www.bbc.com/news/uk-england-london-13823498 |title=London Transport Museum plans 1938 Tube train ride |date=20 June 2011 |access-date=27 August 2020 |publisher=[[BBC News]] |url-status=live |archive-url=https://web.archive.org/web/20200827160803/https://www.bbc.com/news/uk-england-london-13823498 |archive-date=27 August 2020}}</ref>

==List of stations==
{{Piccadilly line RDT|collapsed=yes}}
[[File:Step-free access notification (Piccadilly line).png|thumb|Notice found inside all Piccadilly line trains explaining step-free access]]
[[File:Going to Covent Garden? notification.png|thumb|Notice found inside all Piccadilly line trains explaining alternative routes to Covent Garden]]

===Open stations===

====Main route====
{| class="wikitable"
|-
! Station !! Image !! Opened !! Additional information
|-
| {{stl|London Underground|Cockfosters}} {{access icon}}||[[File:Cockfosters Tube Station 2007.jpg|100px]] || 31 July 1933{{sfn|Horne|2007|p=90}} || ''Terminus'' {{ref|map 1|map 1}}
|-
| {{stl|London Underground|Oakwood}} {{access icon}} || [[File:Oakwood tube station better.jpg|100px]] || rowspan="2" | 13 March 1933{{sfn|Horne|2007|p=90}} || Opened as Enfield West, (East Barnet was initially proposed, name was changed before opening) it was renamed Enfield West (Oakwood) on 3 May 1934. It was renamed to its present name on 1 September 1946.{{sfn|Horne|2007|p=68}} {{ref|map 2|map 2}}
|-
| {{stl|London Underground|Southgate}} || [[File:Southgate station building2.JPG|100px]] || {{ref|map 3|map 3}}
|-
| {{stl|London Underground|Arnos Grove}} || [[File:Arnos Grove stn building.JPG|100px]] || 19 September 1932{{sfn|Horne|2007|p=90}} || {{ref|map 4|map 4}}
|-
| colspan="4" | Tunnel section starts
|-
| {{stl|London Underground|Bounds Green}} || [[File:Bounds Green stn building.jpg|100px]] || rowspan="4" | 19 September 1932{{sfn|Horne|2007|p=90}} || {{ref|map 5|map 5}}
|-
| {{stl|London Underground|Wood Green}} || [[File:Wood Green tube station 070414.JPG|100px]] || {{ref|map 6|map 6}}
|-
| {{stl|London Underground|Turnpike Lane}} || [[File:Turnpike Lane stn building.JPG|100px]] || {{ref|map 7|map 7}}
|-
| {{stl|London Underground|Manor House}} || [[File:Manor House stn main entrance.JPG|100px]] || {{ref|map 8|map 8}}
|-
| {{stl|London Underground|Finsbury Park}} {{rail-interchange|gb|rail}} {{rail-interchange|london|thameslink}} {{access icon}} || [[File:Finsbury Park tube stn entrance Station Place.JPG|100px]] || 1 July 1861{{sfn|Butt|1995|p=208}} || Piccadilly line platforms opened on 15 December 1906.{{sfn|Wolmar|2005|p=181}} Cross-platform interchange with [[Victoria line]],{{sfn|Day|Reed|2010|p=167}} interchange with [[National Rail]] Services. {{ref|map 9|map 9}}
|-
| {{stl|London Underground|Arsenal}} || [[File:Arsenal station entrance.JPG|100px]] || rowspan="3" | 15 December 1906{{sfn|Wolmar|2005|p=181}} || Opened as Gillespie Road; renamed Arsenal (Highbury Hill) 31 October 1932;<ref name="arsenal_469699">{{cite web | url=http://www.thearsenalhistory.com/?p=12035 | title=Arsenal Underground Station Renamed Earlier Than Believed | work=TheArsenalHistory.com |date=31 October 2015 |access-date=22 August 2020 |url-status=live |archive-url=https://web.archive.org/web/20200822160845/http://www.thearsenalhistory.com/?p=12035 |archive-date=22 August 2020}}</ref> the suffix was later dropped in 1960{{sfn|Rose|1999}} {{ref|map 10|map 10}}
|-
| {{stl|London Underground|Holloway Road}} || [[File:Holloway Road stn building.JPG|100px]] || {{ref|map 11|map 11}}
|-
| {{stl|London Underground|Caledonian Road}} {{access icon}} || [[File:Caledonian Road stn building.JPG|100px]] || {{ref|map 12|map 12}}
|-
| {{stl|London Underground|King's Cross St Pancras}} {{access icon}} {{rail-interchange|gb|rail}} {{rail-interchange|london|thameslink}} {{rail-interchange|eurostar|}}|| [[File:King's Cross St Pancras tube stn Euston Rd NE entrance.JPG|100px]] || 10 January 1863{{sfn|Butt|1995|p=134}} || Opened as "King's Cross", it was renamed "King's Cross for St. Pancras" in 1927. The station was renamed again in 1933 to its present name.{{sfn|Butt|1995|p=134}} The Piccadilly line platforms opened on 15 December 1906;{{sfn|Wolmar|2005|p=181}} interchange with [[Circle line (London Underground)|Circle]], [[Hammersmith & City line|Hammersmith & City]], [[Metropolitan line|Metropolitan]], [[Northern line|Northern]] and Victoria lines, National Rail Services {{ref|map 13|map 13}}
|-
| {{stl|London Underground|Russell Square}} || [[File:Russell Square station.jpg|100px]] || rowspan="2" | 15 December 1906{{sfn|Wolmar|2005|p=181}} || {{ref|map 14|map 14}}
|-
| {{stl|London Underground|Holborn}} || [[File:Holborn Tube Station - April 2006.jpg|100px]] || Opened as Holborn (Kingsway), suffix gradually dropped until 1960.{{sfn|Rose|1999}} Interchange with [[Central line (London Underground)|Central line]] {{ref|map 15|map 15}}
|-
| {{stl|London Underground|Covent Garden}} || [[File:Covent Garden stn building.JPG|100px]] || 11 April 1907{{sfn|Rose|1999}} || {{ref|map 16|map 16}}
|-
| {{stl|London Underground|Leicester Square}} || [[File:Leicester Square stn northwest entrance.JPG|100px]] || 15 December 1906{{sfn|Wolmar|2005|p=181}} || Interchange with Northern line {{ref|map 17|map 17}}
|-
| {{stl|London Underground|Piccadilly Circus}} || [[File:Piccadilly Circus main spot and station subway.jpg|100px]] || 10 March 1906{{sfn|Rose|1999}} || Interchange with [[Bakerloo line]] {{ref|map 18|map 18}}
|-
| {{stl|London Underground|Green Park}} {{access icon}} || [[File:Green Park stn building.JPG|100px]] || rowspan="3" | 15 December 1906{{sfn|Wolmar|2005|p=181}} || Opened as Dover Street;{{sfn|Wolmar|2005|p=181}} renamed 18 September 1933.{{sfn|Connor|2006|p=106}} Interchange with [[Jubilee line|Jubilee]] and Victoria lines {{ref|map 19|map 19}}
|-
| {{stl|London Underground|Hyde Park Corner}} || [[File:Hyde Park Corner stn southwest entrance.JPG|100px]] || {{ref|map 20|map 20}}
|-
| {{stl|London Underground|Knightsbridge}} || [[File:Knightsbridge station east entrance.JPG|100px]] || {{ref|map 21|map 21}}
|-
| {{stl|London Underground|South Kensington}} || [[File:South Kensington station.jpg|100px]] || rowspan="2" | 1 October 1868{{sfn|Rose|1999}} || Piccadilly line services began on 8 January 1907;{{sfn|Rose|1999}} interchange with Circle and [[District line|District]] lines {{ref|map 22|map 22}}
|-
| {{stl|London Underground|Gloucester Road}} || [[File:GloucesterRoadTube.jpg|100px]] || Piccadilly line services began on 15 December 1906;{{sfn|Wolmar|2005|p=181}} interchange with Circle and District lines {{ref|map 23|map 23}}
|-
| {{stl|London Underground|Earl's Court}} {{access icon}} || [[File:EarlsCourtEntrance2.jpg|100px]] || 30 October 1871{{sfn|Rose|2007}} || Piccadilly line services began on 15 December 1906;{{sfn|Wolmar|2005|p=181}} interchange with District line {{ref|map 24|map 24}}
|-
| colspan="4" | Tunnel section ends
|-
| {{stl|London Underground|Barons Court}} || [[File:Barons-court-tube.jpg|100px]] || 9 October 1905{{sfn|Horne|2006|p=46}} || Piccadilly line services began on 15 December 1906;{{sfn|Wolmar|2005|p=181}} cross-platform interchange with District line{{sfn|Horne|2007|pp=51–56}} {{ref|map 25|map 25}}
|-
| {{stl|London Underground|Hammersmith|line=District}} {{access icon}} || [[File:Hammersmith entrance District and Piccadilly lines.jpg|100px]] || 9 September 1874{{sfn|Horne|2006|p=15}} || Piccadilly line services began on 15 December 1906;{{sfn|Wolmar|2005|p=181}} cross-platform interchange with District line,{{sfn|Horne|2007|pp=51–56}}<ref name=culgpiccadilly /> interchange with Circle and Hammersmith & City lines {{ref|map 26|map 26}}
|-
| {{stl|London Underground|Turnham Green}} || [[File:Turnham Green stn building.JPG|100px]] || 1 January 1869{{sfn|Horne|2006|p=17}} || First served by the Piccadilly line on 23 June 1963;<ref name=culgpiccadilly /> interchange with District line. Trains only call here early in the morning and after 22:30 each evening.<ref name=luwttpicc2020 /> {{ref|map 27|map 27}}
|-
| {{stl|London Underground|Acton Town}} {{access icon}} || [[File:ActonTown1.jpg|100px]] || 1 July 1879{{sfn|Rose|2007}} || Opened as Mill Hill Park, renamed on 1 October 1910.{{sfn|Horne|2006|p=48}} Piccadilly line services began on 4 July 1932; cross-platform interchange with District line{{sfn|Horne|2006|p=57}} {{ref|map 28|map 28}}
|}

====Heathrow branch====
{| class="wikitable"
|-
|colspan="5" | '''Continuing from Acton Town'''
|-
! Station !! Image !! Opened !! Piccadilly line service began !! Additional information
|-
| {{stl|London Underground|South Ealing}} || [[File:South Ealing stn building.JPG|100px]] || 1 May 1883{{sfn|Horne|2007|p=42}} || 29 April 1935{{sfn|Horne|2007|p=58}} || Off-peak Piccadilly line services began on 29 April 1935, while peak services came in May 1942.{{sfn|Horne|2007|p=59}} {{ref|map 29|map 29}}
|-
| {{stl|London Underground|Northfields}} || [[File:Northfields station building.JPG|100px]] || 16 April 1908{{sfn|Horne|2007|p=46}} || 9 January 1933{{sfn|Horne|2007|p=58}} || Opened as Northfield (Ealing), renamed Northfields & Little Ealing on 11 December 1911.{{sfn|Horne|2007|p=46}} The station was relocated to the east on 19 May 1932, enabling a depot to be constructed west of the new location.{{sfn|Connor|2001|p=115}} {{ref|map 30|map 30}}
|-
| {{stl|London Underground|Boston Manor}} || [[File:Boston Manor stn building.JPG|100px]] || 1 May 1883{{sfn|Horne|2007|p=42}} || 13 March 1933{{sfn|Horne|2007|p=58}} || Opened as Boston Road, renamed 11 December 1911{{sfn|Horne|2007|p=42}}<ref>{{cite web |url=http://www.lurs.org.uk/02%20oct%20PICCADILLY%20TO%20THE%20WEST.pdf |last=Stuart |first=Eric |title=Piccadilly to the West |access-date=22 August 2020 |publisher=London Underground Railway Society |url-status=live |page=19 |work=Points of Interest |archive-url=https://web.archive.org/web/20181204111904/http://www.lurs.org.uk/02%20oct%20PICCADILLY%20TO%20THE%20WEST.pdf |archive-date=4 December 2018}}</ref> {{ref|map 31|map 31}}
|-
| {{stl|London Underground|Osterley}} {{access icon}}|| [[File:Osterley station building2.JPG|100px]] || colspan="2" | 25 March 1934{{sfn|Rose|1999}} || Replacement of [[Osterley & Spring Grove tube station|Osterley & Spring Grove station]]{{sfn|Rose|1999}} {{ref|map 32|map 32}}
|-
| {{stl|London Underground|Hounslow East}} {{access icon}} || [[File:Hounslow East stn building.JPG|100px]] || 2 May 1909{{sfn|Horne|2007|p=46}} || rowspan="2" | 13 March 1933{{sfn|Horne|2007|p=58}} || Opened as Hounslow Town, renamed 1 December 1925{{sfn|Horne|2007|p=54}} {{ref|map 33|map 33}}
|-
| {{stl|London Underground|Hounslow Central}} || [[File:Hounslow Central building.JPG|100px]] || 1 April 1886{{sfn|Horne|2007|p=42}} || Opened as Heston–Hounslow, renamed 1 December 1925{{sfn|Horne|2007|p=54}} {{ref|map 34|map 34}}
|-
|colspan="5" | Start of tunnel section
|-
| {{stl|London Underground|Hounslow West}} {{access icon}} || [[File:Hounslow West stn building.JPG|100px]] || 21 July 1884{{sfn|Horne|2007|p=42}} || 13 March 1933{{sfn|Horne|2007|p=58}} || Opened as Hounslow Barracks, renamed 1 December 1925.{{sfn|Horne|2007|p=54}} Resited 19 July 1975{{sfn|Horne|2007|p=121}} {{ref|map 35|map 35}}
|-
| {{stl|London Underground|Hatton Cross}} || [[File:Hatton Cross stn northern entrance.JPG|100px]] || colspan="2" | 19 July 1975{{sfn|Horne|2007|p=121}} || {{ref|map 36|map 36}}
|-
| {{stl|London Underground|Heathrow Terminal 4}} {{access icon}} {{Rint|london|elizabeth}} (not connected to tube station) {{rint|air|link=Heathrow Airport}}
| [[File:Heathrow Terminal 4 tube entrance.JPG|100px]] || colspan="2" | 12 April 1986{{sfn|Horne|2007|p=126}} || {{ref|map 37|map 37}}
|-
| {{stl|London Underground|Heathrow Terminals 2 & 3}} {{access icon}} {{Rint|london|elizabeth}} {{Rint|london|heathrowexpress}} (not connected to tube station) {{rint|air|link=Heathrow Airport}}
| [[File:Heathrow Terms 123 entrance.JPG|100px]] || colspan="2" | 16 December 1977{{sfn|Horne|2007|p=121}} || Opened as Heathrow Central;{{sfn|Horne|2007|p=121}} renamed Heathrow Terminals 1, 2, 3 on 12 April 1986;{{sfn|Horne|2007|p=126}} renamed Heathrow Terminals 2 & 3 in January 2016;<ref>{{cite news|title=Heathrow Terminal One deserted ahead of closure next month|url=http://www.itv.com/news/london/2015-05-28/heathrow-terminal-one-deserted-ahead-of-closure-next-month/|access-date=23 March 2018|work=ITV News|date=28 May 2015|archive-url=https://web.archive.org/web/20180315202357/http://www.itv.com/news/london/2015-05-28/heathrow-terminal-one-deserted-ahead-of-closure-next-month/|archive-date=15 March 2018|url-status=live}}</ref> {{ref|map 38|map 38}}
|-
| {{stl|London Underground|Heathrow Terminal 5}} {{access icon}} {{Rint|london|elizabeth}} {{Rint|london|heathrowexpress}} {{rint|air|link=Heathrow Airport}}
| [[File:Heathrow Terminal 5 Underground entrance.JPG|100px]] || colspan="2" | 27 March 2008<ref name=heathrowt5pressrelease/> || ''Terminus'' {{ref|map 39|map 39}}
|-
|colspan="5" | <!--This section is a loop with a branch: trains go to Hatton Cross, then to either Terminal 4, round to Terminals 2 & 3 and then carry on back to Hatton Cross, or to Terminals 2 & 3, then Terminal 5 then reverse.-->
Train services alternate between Terminals 2,3 & 5 and Terminals 4 & 2,3 since 2008.<ref name=luwttpicc2020 /><ref>{{cite web |title=Piccadilly line's new timetable |publisher= Transport for London |date=8 January 2008 |url= http://www.tfl.gov.uk/corporate/media/newscentre/7156.aspx |archive-url= https://web.archive.org/web/20080227081200/http://www.tfl.gov.uk/corporate/media/newscentre/7156.aspx |archive-date=27 February 2008}}</ref>
|}

====Uxbridge branch====
{| class="wikitable"
|-
|colspan="5" | '''Continuing from Acton Town'''
|-
! Station !! Image !! Opened !! Piccadilly line service began !! Additional information
|-
| {{stl|London Underground|Ealing Common}} || [[File:Ealing Common stn building.JPG|100px]] || 1 July 1879{{sfn|Rose|1999}} || rowspan="7" | 4 July 1932{{sfn|Horne|2007|p=57}} || Shared platforms with District line<ref name=cartomap /> {{ref|map 40|map 40}}
|-
| {{stl|London Underground|North Ealing}} || [[File:North Ealing stn building.JPG|100px]] || 23 June 1903{{sfn|Horne|2006|p=39}} || {{ref|map 41|map 41}}
|-
| {{stl|London Underground|Park Royal}} || [[File:Park Royal stn building.JPG|100px]] || 6 July 1931{{sfn|Rose|1999}} || Replacement of [[Park Royal & Twyford Abbey tube station|Park Royal & Twyford Abbey station]]; renamed Park Royal (Hanger Hill) 1 March 1936; reverted to original in 1947{{sfn|Rose|1999}} {{ref|map 42|map 42}}
|-
| {{stl|London Underground|Alperton}} || [[File:Alperton station building.JPG|100px]] || rowspan="4" | 28 June 1903{{sfn|Rose|2007}} || Opened as Perivale–Alperton by the District line; renamed 7 October 1910{{sfn|Rose|1999}} {{ref|map 43|map 43}}
|-
| {{stl|London Underground|Sudbury Town}} {{access icon}} || [[File:Sudbury Town stn main entrance.JPG|100px]] || {{ref|map 44|map 44}}
|-
| {{stl|London Underground|Sudbury Hill}} {{access icon}} ({{rail-interchange|gb|rail}} <small>{{Stnlnk|Sudbury Hill Harrow}}</small>) || [[File:Sudbury Hill stn building.JPG|100px]] || {{ref|map 45|map 45}}
|-
| {{stl|London Underground|South Harrow}} || [[File:South Harrow stn southern entrance.JPG|100px]] || Platforms moved approximately {{convert|200|ft|m}} to the west in 1935{{sfn|Horne|2007|p=61}} {{ref|map 46|map 46}}
|-
|colspan="5" | Shared section with [[Metropolitan line]]
|-
| {{stl|London Underground|Rayners Lane}} || [[File:Rayners Lane stn building.JPG|100px]] || rowspan="2" | 26 May 1906{{sfn|Horne|2007|p=45}} || rowspan="7" | 23 October 1933{{sfn|Horne|2007|p=58}} || {{ref|map 47|map 47}}
|-
| {{stl|London Underground|Eastcote}} || [[File:Eastcote tube station 1.jpg|100px]] || {{ref|map 48|map 48}}
|-
| {{stl|London Underground|Ruislip Manor}} || [[File:Ruislip Manor tube station 1.jpg|100px]] || 5 August 1912{{sfn|Horne|2007|p=45}} || {{ref|map 49|map 49}}
|-
| {{stl|London Underground|Ruislip}} || [[File:Ruislip station building.JPG|100px]] || 4 July 1904{{sfn|Horne|2007|p=45}} || {{ref|map 50|map 50}}
|-
| {{stl|London Underground|Ickenham}} {{access icon}} || [[File:Ickenham tube station 1.jpg|100px]] || 25 September 1905{{sfn|Horne|2007|p=45}} || {{ref|map 51|map 51}}
|-
| {{stl|London Underground|Hillingdon}} {{access icon}} || [[File:Hillingdon stn entrance.JPG|100px]] || 10 December 1923{{sfn|Horne|2007|p=45}} || The station was named Hillingdon (Swakeleys) momentarily from the 1930s to the 1950s.{{sfn|Wallinger|Self|Warner|Wolmar|2014|p=60}}  It was relocated in 1992 to make way for the [[A40 road in London|A40]] expansion.{{sfn|Horne|2007|p=130}} {{ref|map 52|map 52}}
|-
| {{stl|London Underground|Uxbridge}} {{access icon}} || [[File:Uxbridge station entrance.JPG|100px]] || 4 July 1904{{sfn|Horne|2007|p=45}} || ''Terminus''; relocated 4 December 1938{{sfn|Horne|2007|p=61}} {{ref|map 53|map 53}}
|}

===Closed stations===
[[File:Aldwych branch (en).svg|thumb|upright=1.35|The Aldwych branch]]
* {{stl|London Underground|Aldwych}} opened on 30 November 1907 as Strand. It was renamed Aldwych on 9 May 1915.{{sfn|Rose|1999}} The possibility of extending the branch to [[Waterloo tube station|Waterloo]] was discussed, but the scheme never proceeded.<ref>{{Cite news |title=More tube lines discussed: Easing travel load |newspaper=The Times |location=London |date=27 April 1965 |page=7}}</ref> Aldwych was closed on 30 September 1994. It is now regularly used by film makers.{{sfn|Connor|2001|p=99–101}}
* {{stl|London Underground|Brompton Road}} opened 15 December 1906; closed 30 July 1934, between {{stl|London Underground|Knightsbridge}} and {{stl|London Underground|South Kensington}}.{{sfn|Rose|1999}}
* {{stl|London Underground|Down Street}} opened 15 December 1906; closed 21 May 1932, between {{stl|London Underground|Green Park}} and {{stl|London Underground|Hyde Park Corner}}.{{sfn|Rose|1999}}
* [[Osterley & Spring Grove tube station|Osterley & Spring Grove]] first served on 13 March 1933;{{sfn|Horne|2006|p=60}} closed 24 March 1934, between {{stl|London Underground|Boston Manor}} and {{stl|London Underground|Hounslow East}}. It was replaced by {{stl|London Underground|Osterley}}.{{sfn|Rose|1999}}
* {{stl|London Underground|Park Royal & Twyford Abbey}} opened 23 June 1903; closed 5 July 1931. Although on the route of the current Piccadilly line, a short distance north of the present {{stl|London Underground|Park Royal}} station, it was never served by Piccadilly line trains. It was opened by the District Railway, and was closed and replaced by Park Royal{{sfn|Rose|1999}} before the Piccadilly line started running trains to South Harrow in 1932.{{sfn|Horne|2006|p=60}}
* {{stl|London Underground|York Road}} opened 15 December 1906;{{sfn|Wolmar|2005|p=181}} closed 19 September 1932, between {{stl|London Underground|King's Cross St Pancras}} and {{stl|London Underground|Caledonian Road}}.{{sfn|Lee|1966|p=22}} It was about 600&nbsp;m north of King's Cross St Pancras.{{sfn|Day|Reed|2010|p=111}}

==Future upgrade and proposals==
The Piccadilly line is to be upgraded under the [[New Tube for London]] scheme, involving new trains as well as new signalling, increasing the line's capacity by some {{nowrap|24 per cent}} and reducing journey times by one fifth.<ref>{{cite web |title=Tube improvement plan: Piccadilly line |url=http://www.tfl.gov.uk/corporate/projectsandschemes/18098.aspx |publisher=Transport for London |access-date=29 December 2013 |archive-date=18 May 2011 |archive-url=https://web.archive.org/web/20110518090304/http://www.tfl.gov.uk/corporate/projectsandschemes/18098.aspx |url-status=dead }}</ref> Bids for new rolling stock were originally submitted in 2008. However, after the acquisition of [[Tube Lines]] by Transport for London in June 2010, this order was cancelled and the upgrade postponed.<ref name="ford201010">{{Cite news |last=Ford |first=Roger |date=October 2010 |title=Rolling stock famine deepens as Bombardier feasts on past orders |work=Modern Railways |volume=67 |issue=745 |page=22 |location= London}}</ref>

LUL then invited [[Alstom]], [[Bombardier Transportation|Bombardier]] and [[Siemens Mobility]] to develop a new concept of lightweight, low-energy, semi-articulated train for the deep-level lines, provisionally called "Evo" (for 'evolution'). Siemens publicised an outline design featuring air-conditioning and battery power to enable the train to run on to the next station if [[Fourth rail|third and fourth rail]] power were lost. It would have a lower floor and {{nowrap|11 per cent}} higher passenger capacity than the present tube stock.<ref name="waboso">{{cite news |title=Transforming the tube |author=Waboso, David |work=Modern Railways |location=London |date=December 2010 |page=44}}</ref>
There would be a weight saving of 30&nbsp;tonnes, and the trains would be {{nowrap|17 per cent}} more energy-efficient with air-conditioning included, or {{nowrap|30 per cent}} more energy-efficient without it.<ref>{{cite news |url=https://www.railwaygazette.com/nc/news/single-view/view/siemens-unveils-london-underground-concept-train.html |work=Railway Gazette International |location =London |title= Siemens unveils London Underground concept train |date=20 June 2011 |access-date=31 October 2020 |archive-date=31 October 2020 |archive-url=https://web.archive.org/web/20201031063602/https://www.railwaygazette.com/nc/news/single-view/view/siemens-unveils-london-underground-concept-train.html}}</ref> Siemens Mobility was awarded a £1.5 billion contract in June 2018 to produce the new trains at a [[Siemens Goole|planned factory in Goole]], [[East Yorkshire]].<ref name=Siemens2018>{{cite news |title=East Yorkshire factory wins £1.5bn Tube train deal |url=https://www.bbc.co.uk/news/uk-england-humber-44496526 |access-date=15 June 2018 |work=BBC News |date=15 June 2018}}</ref>

The intention is for the new trains to eventually operate on the Bakerloo, Central, Piccadilly and Waterloo & City lines.<ref>{{cite news |title= Siemens reveals innovative air-con for deep Tube trains |page= 12 |work= Rail |location =Peterborough |issue=673 |date=29 June 2011}}</ref> Resignalling work on the Piccadilly line was to begin in 2019<ref>{{cite web |publisher= Transport for London |date= December 2013 |url= http://www.tfl.gov.uk/assets/downloads/corporate/tfl-business-plan-december-2013.pdf |title= Business Plan 2013 |page= 35 |access-date= 9 January 2014 |archive-date= 11 February 2014 |archive-url= https://web.archive.org/web/20140211030139/http://www.tfl.gov.uk/assets/downloads/corporate/tfl-business-plan-december-2013.pdf |url-status= dead }}</ref><ref>{{cite news |last1=Gelder |first1=Sam |title=Piccadilly line trains still run by 'obsolete' signalling system from the 1950s |url=https://www.islingtongazette.co.uk/news/piccadilly-line-trains-still-run-by-obsolete-signalling-system-from-3792756 |access-date=4 March 2021 |work=[[Islington Gazette]] |date=15 May 2018}}</ref> but this has since been shelved because of lack of funds.<ref>{{cite web |last1=Rogers |first1=Alexandra |title=Treasury rebuffed TfL bid for Piccadilly line funds in spending round |url=https://www.cityam.com/treasury-rebuffed-tfl-bid-for-piccadilly-line-funds-in-spending-round/ |website=CityAM |access-date=4 March 2021 |date=22 September 2019}}</ref> New trains were due to enter service in 2023,<ref name=Siemens2018/> bringing an increase in peak frequencies from 24 to 27 tph.<ref name="railtechntfl">{{cite news |date=21 November 2018 |title=London Underground awards £1.5bn deal to Siemens for 94 Tube trains |work=Railway Technology |url=https://www.railway-technology.com/news/london-siemens-94-tube-trains/ |url-status=live |access-date=27 August 2020 |archive-url=https://web.archive.org/web/20200827162739/https://www.railway-technology.com/news/london-siemens-94-tube-trains/ |archive-date=27 August 2020}}</ref> In March 2021, it was reported that the new trains would not enter service before 2025, that the increase in peak frequency from 24 to 27 tph would not take place until about 2027, and that any further increase to 30 tph would be delayed until the signalling system is upgraded, for which funds are not currently available.<ref>{{cite news|last=Lydall|first=Ross|url=https://www.standard.co.uk/news/transport/design-new-piccadilly-line-trains-unveiled-tfl-b922086.html|title=First look: TfL unveils design of new Piccadilly line trains|work=[[Evening Standard]]|location=London|date=4 March 2021|access-date=4 March 2021}}</ref><ref>{{cite web |title=Improving the trains |url=https://tfl.gov.uk/campaign/tube-improvements/what-we-are-doing/improving-the-trains |website=Transport for London |access-date=4 March 2021 |url-status=live |archive-url=https://web.archive.org/web/20210324011843/https://tfl.gov.uk/campaign/tube-improvements/what-we-are-doing/improving-the-trains |archive-date=24 March 2021}}</ref>

There have previously been some proposals, predominantly by [[Slough Borough Council]], to extend the line towards [[Slough railway station]] from [[Heathrow Terminal 5 station]]. A number of routes have been proposed, and the main ones pass very close to but do not call at [[Windsor & Eton Central railway station|Windsor]].<ref name="thamesvalleychamber.co.uk">{{cite web |url=http://www.thamesvalleychamber.co.uk/uploads/Policy/SBCpresentationSep09.pdf |title=Slough Borough Council presentation |publisher=Thames Valley Chamber of Commerce Group |access-date=29 December 2013 |url-status = dead|archive-url=https://web.archive.org/web/20130809230423/http://www.thamesvalleychamber.co.uk/uploads/Policy/SBCpresentationSep09.pdf |archive-date=9 August 2013 }}</ref> The current thinking, and most viable options are to support a western access link diverging from the Great Western Main Line just east of [[Langley station]].<ref>{{Cite web |url=https://aec.heathrowconsultation.com/wp-content/uploads/sites/5/2019/06/Preferred-Masterplan-Hi-Res.pdf|title=Preferred Masterplan |website=Heathrow Airport Expansion Consultation|page=19 |access-date=27 August 2020 |url-status=dead |archive-url=https://web.archive.org/web/20160910101431/https://consultations.networkrail.co.uk/communications/westernraillinktoheathrow/ |archive-date=10 September 2016 |date=2016}}</ref>

In 2005, a business case was prepared to re-open the disused [[York Road tube station|York Road station]], to serve the [[King's Cross Central]] development and help relieve congestion at King's Cross St Pancras.<ref name="kce_yorkroad">{{cite web |url=http://www.kingscrossenvironment.com/files/york_road_business_case_report__final__2sided.pdf |title=York Road Station Re-opening – Business Case Analysis |year=2005 |publisher=[[Halcrow Group Limited]] |page=6 |archive-url=https://web.archive.org/web/20110726075815/http://www.kingscrossenvironment.com/files/york_road_business_case_report__final__2sided.pdf |archive-date=26 July 2011 |url-status = dead|quote=The objective would be to ensure that public transport users travelling from the KCC development would benefit from travelling via York Road Station rather than using King’s Cross St Pancras Station. This in turn leads to the subobjective of providing congestion relief for King’s Cross St Pancras Station.}}</ref>

==See also==
* [[Fourth rail]]

==Geographical locations==
{{div col|colwidth=25em|small=yes}}
*{{note|map 1|map 1}}Cockfosters – {{Coord|51|39|06|N|000|08|56|W|region:GB_type:railwaystation|name=01 - Cockfosters tube station}}
*{{note|map 2|map 2}}Oakwood – {{Coord|51|38|51|N|000|07|54|W|region:GB_type:railwaystation|name=02 - Oakwood tube station}}
*{{note|map 3|map 3}}Southgate – {{Coord|51|37|57|N|000|07|41|W|region:GB_type:railwaystation|name=03 - Southgate tube station}}
*{{note|map 4|map 4}}Arnos Grove – {{Coord|51|36|59|N|000|08|01|W|region:GB_type:railwaystation|name=04 - Arnos Grove tube station}}
*{{note|map 5|map 5}}Bounds Green – {{Coord|51|36|25|N|000|07|27|W|region:GB_type:railwaystation|name=05 - Bounds Green tube station}}
*{{note|map 6|map 6}}Wood Green – {{Coord|51|35|49|N|000|06|36|W|region:GB_type:railwaystation|name=06 - Wood Green tube station}}
*{{note|map 7|map 7}}Turnpike Lane – {{Coord|51|35|25|N|000|06|10|W|region:GB_type:railwaystation|name=07 - Turnpike Lane tube station}}
*{{note|map 8|map 8}}Manor House – {{Coord|51|34|15|N|000|05|46|W|region:GB_type:railwaystation|name=08 - Manor House tube station}}
*{{note|map 9|map 9}}Finsbury Park – {{Coord|51|33|53|N|000|06|23|W|region:GB_type:railwaystation|name=09 - Finsbury Park station}}
*{{note|map 10|map 10}}Arsenal – {{Coord|51|33|31|N|000|06|21|W|region:GB_type:railwaystation|name=10 - Arsenal tube station}}
*{{note|map 11|map 11}}Holloway Road – {{Coord|51|33|11|N|000|06|43|W|region:GB_type:railwaystation|name=11 - Holloway Road tube station}}
*{{note|map 12|map 12}}Caledonian Road – {{Coord|51|32|54|N|000|07|07|W|region:GB_type:railwaystation|name=12 - Caledonian Road tube station}}
*{{note|map 13|map 13}}King's Cross St Pancras – {{Coord|51|31|49|N|000|07|27|W|region:GB_type:railwaystation|name=13 - King's Cross St Pancras tube station}}
*{{note|map 14|map 14}}Russell Square – {{Coord|51|31|23|N|000|07|28|W|region:GB_type:railwaystation|name=14 - Russell Square tube station}}
*{{note|map 15|map 15}}Holborn – {{Coord|51|31|03|N|000|07|12|W|region:GB_type:railwaystation|name=15 - Holborn tube station}}
*{{note|map 16|map 16}}Covent Garden – {{Coord|51|30|47|N|000|07|27|W|region:GB_type:railwaystation|name=16 - Covent Garden tube station}}
*{{note|map 17|map 17}}Leicester Square – {{Coord|51|30|41|N|000|07|41|W|region:GB_type:railwaystation|name=17 - Leicester Square tube station}}
*{{note|map 18|map 18}}Piccadilly Circus – {{Coord|51|30|36|N|000|08|02|W|region:GB_type:railwaystation|name=18 - Piccadilly Circus tube station}}
*{{note|map 19|map 19}}Green Park – {{Coord|51|30|24|N|000|08|34|W|region:GB_type:railwaystation|name=19 - Green Park tube station}}
*{{note|map 20|map 20}}Hyde Park Corner – {{Coord|51|30|10|N|000|09|10|W|region:GB_type:railwaystation|name=20 - Hyde Park Corner tube station}}
*{{note|map 21|map 21}}Knightsbridge – {{Coord|51|30|06|N|000|09|39|W|region:GB_type:railwaystation|name=21 - Knightsbridge tube station}}
*{{note|map 22|map 22}}South Kensington – {{Coord|51|29|39|N|000|10|26|W|region:GB_type:railwaystation|name=22 - South Kensington tube station}}
*{{note|map 23|map 23}}Gloucester Road – {{Coord|51|29|41|N|000|10|59|W|region:GB_type:railwaystation|name=23 - Gloucester Road tube station}}
*{{note|map 24|map 24}}Earl's Court – {{Coord|51|29|29|N|000|11|41|W|region:GB_type:railwaystation|name=24 - Earl's Court tube station}}
*{{note|map 25|map 25}}Barons Court – {{Coord|51|29|26|N|000|12|49|W|region:GB_type:railwaystation|name=25 - Barons Court tube station}}
*{{note|map 26|map 26}}Hammersmith – {{Coord|51|29|39|N|000|13|30|W|region:GB_type:railwaystation|name=26 - Hammersmith tube station}}
*{{note|map 27|map 27}}Turnham Green – {{Coord|51|29|43|N|000|15|18|W|region:GB_type:railwaystation|name=27 - Turnham Green tube station}}
*{{note|map 28|map 28}}Acton Town – {{Coord|51|30|10|N|000|16|48|W|region:GB_type:railwaystation|name=28 - Acton Town tube station}}
*{{note|map 29|map 29}}South Ealing – {{Coord|51|30|04|N|000|18|26|W|region:GB_type:railwaystation|name=29 - South Ealing tube station}}
*{{note|map 30|map 30}}Northfields – {{Coord|51|29|58|N|000|18|51|W|region:GB_type:railwaystation|name=30 - Northfields tube station}}
*{{note|map 31|map 31}}Boston Manor – {{Coord|51|29|45|N|000|19|30|W|region:GB_type:railwaystation|name=31 - Boston Manor tube station}}
*{{note|map 32|map 32}}Osterley – {{Coord|51|28|53|N|000|21|08|W|region:GB_type:railwaystation|name=32 - Osterley tube station}}
*{{note|map 33|map 33}}Hounslow East – {{Coord|51|28|23|N|000|21|23|W|region:GB_type:railwaystation|name=33 - Hounslow East tube station}}
*{{note|map 34|map 34}}Hounslow Central – {{Coord|51|28|17|N|000|21|59|W|region:GB_type:railwaystation|name=34 - Hounslow Central tube station}}
*{{note|map 35|map 35}}Hounslow West – {{Coord|51|28|25|N|000|23|08|W|region:GB_type:railwaystation|name=35 - Hounslow West tube station}}
*{{note|map 36|map 36}}Hatton Cross – {{Coord|51|28|01|N|000|25|24|W|region:GB_type:railwaystation|name=36 - Hatton Cross tube station}}
*{{note|map 37|map 37}}Heathrow Terminal 4 – {{Coord|51|27|32|N|000|26|46|W|region:GB_type:railwaystation|name=37 - Heathrow Terminal 4 tube station}}
*{{note|map 38|map 38}}Heathrow Terminals 2 & 3 – {{Coord|51|28|16|N|000|27|07|W|region:GB_type:railwaystation|name=38 - Heathrow Terminals 2 & 3 tube station}}
*{{note|map 39|map 39}}Heathrow Terminal 5 – {{Coord|51|28|20|N|000|29|17|W|region:GB_type:railwaystation|name=39 - Heathrow Terminal 5 station}}
*{{note|map 40|map 40}}Ealing Common – {{Coord|51|30|37|N|000|17|17|W|region:GB_type:railwaystation|name=40 - Ealing Common tube station}}
*{{note|map 41|map 41}}North Ealing – {{Coord|51|31|03|N|000|17|19|W|region:GB_type:railwaystation|name=41 - North Ealing tube station}}
*{{note|map 42|map 42}}Park Royal – {{Coord|51|31|37|N|000|17|03|W|region:GB_type:railwaystation|name=42 - Park Royal tube station}}
*{{note|map 43|map 43}}Alperton – {{Coord|51|32|27|N|000|17|59|W|region:GB_type:railwaystation|name=43 - Alperton tube station}}
*{{note|map 44|map 44}}Sudbury Town – {{Coord|51|33|03|N|000|18|56|W|region:GB_type:railwaystation|name=44 - Sudbury Town tube station}}
*{{note|map 45|map 45}}Sudbury Hill – {{Coord|51|33|25|N|000|20|11|W|region:GB_type:railwaystation|name=45 - Sudbury Hill tube station}}
*{{note|map 46|map 46}}South Harrow – {{Coord|51|33|53|N|000|21|08|W|region:GB_type:railwaystation|name=46 - South Harrow tube station}}
*{{note|map 47|map 47}}Rayners Lane – {{Coord|51|34|31|N|000|22|17|W|region:GB_type:railwaystation|name=47 - Rayners Lane tube station}}
*{{note|map 48|map 48}}Eastcote – {{Coord|51|34|36|N|000|23|49|W|region:GB_type:railwaystation|name=48 - Eastcote tube station}}
*{{note|map 49|map 49}}Ruislip Manor – {{Coord|51|34|24|N|000|24|45|W|region:GB_type:railwaystation|name=49 - Ruislip Manor tube station}}
*{{note|map 50|map 50}}Ruislip – {{Coord|51|34|17|N|000|25|16|W|region:GB_type:railwaystation|name=50 - Ruislip tube station}}
*{{note|map 51|map 51}}Ickenham – {{Coord|51|33|43|N|000|26|31|W|region:GB_type:railwaystation|name=51 - Ickenham tube station}}
*{{note|map 52|map 52}}Hillingdon – {{Coord|51|33|14|N|000|27|00|W|region:GB_type:railwaystation|name=52 - Hillingdon tube station}}
*{{note|map 53|map 53}}Uxbridge – {{Coord|51|32|45|N|000|28|42|W|region:GB_type:railwaystation|name=53 - Uxbridge tube station}}
*{{note|map 54|map 54}}Cockfosters Depot – {{Coord|51|38|56|N|000|08|25|W|region:GB_type:railwaystation|name=54 - Cockfosters Depot}}
*{{note|map 55|map 55}}Northfields Depot – {{Coord|51|29|50|N|000|19|14|W|region:GB_type:railwaystation|name=55 - Northfields Depot}}
{{div col end}}
{{GeoGroup}}

==Notes and references==
===Notes===
{{Reflist|group=note}}

===References===
{{reflist}}

===Bibliography===
{{refbegin|30em}}
* {{Cite book |last1=Barker |first1=T.C. |last2=Robbins|first2=Michael |title=A History of London Transport: Volume two – the Twentieth Century to 1970 |location=London |publisher=George Allen & Unwin Ltd. |year=1974 |isbn=0-04-385067-7 }}
* {{cite book |last=Badsey-Ellis |first=Antony |title=London's Lost Tube Schemes |publisher=Capital Transport |isbn=1-85414-293-3 |year=2005 }}
* {{cite book |last=Badsey-Ellis |first=Antony |title=Building London's Underground: From Cut-and Cover to Crossrail |year=2016 |publisher=Capital Transport |isbn=978-1-8541-4397-6 }}
* {{cite book |first=J Graeme|last=Bruce|title=The London Underground Tube Stock|publisher=Ian Allan and London Transport Museum|location=Shepperton|year=1988|isbn=978-0-7110-1707-8}}
* {{butt-stations}}
* {{cite book |last1=Cherry |first1=Bridget |last2=Pevsner |first2=Nikolaus |author-link2=Nikolaus Pevsner |url = https://books.google.com/books?id=rVHqBvtuLyMC |title=London 3: North West |series=[[Pevsner Architectural Guides|The Buildings of England]] |year=1991 |publisher=[[Yale University Press]] |isbn=978-0-300-09652-1 |access-date=19 August 2020 }}
* {{cite book | last=Connor | first=J.E. | title=London's Disused Underground Stations | year=2001 | orig-year=1999 | publisher=Capital Transport | isbn=1-85414-250-X }}
* {{cite book | first=J. E. | last=Connor | title=London's Disused Underground Stations | publisher=Capital Transport | year=2006 |orig-year=1999 | edition=2nd (revised) |isbn=978-1-85414-250-4 }}
* {{Cite book |last=Croome |first=Desmond F. |title=The Piccadilly Line – An Illustrated History |location=London |publisher=Capital Transport Publishing |year=1998 |isbn=1-85414-192-9 }}
* {{cite book |last1=Croome|first1=Desmond F.|last2=Jackson|first2=Alan Arthur|title=Rails Through the Clay: A History of London's Tube Railways|year=1993|publisher=Capital Transport|isbn=978-1-85414-151-4}}
* {{cite book |last1=Day |first1=John R. |last2=Reed |first2=John |title=The Story of London's Underground |edition=10th |year=2008 |orig-year=1963 |publisher=Capital Transport |isbn=978-1-85414-316-7 }}
* {{cite book |last1=Day |first1=John R |last2=Reed |first2=John |title=The Story of London's Underground |edition=11th |year=2010 |orig-year=1963 |publisher=Capital Transport |isbn=978-1-85414-341-9 }}
* {{cite book |first=H G |last=Follenfant|title=Reconstructing London's Underground|year=1974|publisher=London Transport Executive|isbn=978-0-85329-039-1}}
* {{cite book |last=Hardy |first=Brian |title=Underground Train File: Tube Stock 1933-1959 |year=2001 |publisher=Capital Transport |location=Harrow Weald |isbn=1-85414-235-6 }}
* {{cite book |last=Harris |first=Cyril M. |title = What's in a name? |publisher = Capital Transport |orig-year=1977 |year=2006 |isbn=1-85414-241-0 }}
* {{cite book | first=Mike |last=Horne |title=The Jubilee Line |year=2000 |publisher=Capital Transport |isbn=978-1-85414-220-7 }}
* {{cite book |last=Horne|first=Mike|title=The Metropolitan Line|year=2003|publisher=Capital Transport|isbn=1-85414-275-5 |url-access=registration|url=https://archive.org/details/metropolitanline00mike }}
* {{cite book |last=Horne |first=Mike |title=The District Line: An Illustrated History |year=2006 |publisher=Capital Transport |isbn=1-85414-292-5 }}
* {{Cite book |last=Horne |first=Mike |title=The Piccadilly Tube – A History of the First Hundred Years |location=London |publisher=Capital Transport |year=2007 |isbn=978-1-85414-305-1 }}
* {{cite book |last=Karol |first=Eitan |title=Charles Holden: Architect |publisher=Shaun Tyas |year=2007 |isbn=978-1-900289-81-8 }}
* {{cite book |url=https://books.google.com/books?id=b409AAAAIAAJ&pg=PA123 |title=London's lost railways |last=Klapper|first=Charles |publisher =Routledge & Kegan Paul |location =London |year=1976 |oclc=487714609|isbn=9780710083784 }}
* {{Cite book |last=Lee |first=Charles E. |title=Sixty Years of the Piccadilly |location=London |publisher=London Transport |year=1966 }}
* {{Cite book |last=Lee |first=Charles E. |title=The Piccadilly Line: a brief history |location=London |publisher=London Transport |year=1973 |isbn=0-85329-042-3 }}
* {{cite book |last=Martin | first=Andrew |title=Underground, Overground: A Passenger's History of the Tube |publisher=Profile Books |year=2012 |isbn=978-1-84765-807-4 }}
* {{cite web |last=Powers |first=Alan |url=https://www.oxfordartonline.com/subscriber/article/grove/art/T038611 |author-link=Alan Powers |title=Holden, Charles (Henry) |work=[[Grove Art Online]] |publisher=[[Oxford University Press]] |year=2007 |access-date=25 September 2010 |url-access=subscription }} (Wikipedia Library ID accepted)
* {{cite book |last=Rose |first=Douglas |title=The London Underground, A Diagrammatic History |year=1999 |publisher=Douglas Rose/Capital Transport |isbn=1-85414-219-4 }}
* {{cite book |last=Rose |first=Douglas |title=The London Underground: A Diagrammatic History |edition=8th |date=December 2007 |orig-year=1980 |publisher=Capital Transport |location=Harrow Weald |isbn=978-1-85414-315-0 }}
* {{cite book |last=Simpson|first=Bill|title=A History of the Metropolitan Railway. Volume 1: The Circle and Extended Lines to Rickmansworth.|publisher=Lamplight Publications|year=2003|isbn=1-899246-07-X}}
* {{cite book |title=Labyrinth: A Journey Through London's Underground by Mark Wallinger |last1=Wallinger |first1=Mark |last2=Self |first2=Will |last3=Warner |first3=Marina |last4=Wolmar |first4=Christian |last5=Bal |first5=Thierry |last6=Coysh |first6=Louise |last7=Dillon |first7=Tamsin |date=6 October 2014 |publisher=Art / Books |isbn=978-1-90897-016-9 }}
* {{cite book |last=Wolmar |first=Christian |title = The Subterranean Railway: How the London Underground Was Built and How It Changed the City Forever |publisher = Atlantic Books |isbn=1-84354-023-1 |orig-year=2004 |year = 2005 }}
* {{cite book |title=The Victoria Line : Report by the London Travel Committee to the Minister of Transport and Civil Aviation|publisher=Her Majesty's Stationery Office|year=1959|url=https://archive.org/details/op1265392-1001|ref={{harvid|HMSO|1959}}}}
{{refend}}

==External links==
{{Commons category}}
{{Attached KML|display=title,inline}}
* {{Official website}}
* {{cite web |title=Piccadilly line facts |url=http://www.tfl.gov.uk/corporate/modesoftransport/londonunderground/keyfacts/13175.aspx |work=London Underground — Key Facts |publisher=Transport for London |access-date=12 April 2011 |archive-date=10 February 2014 |url-status = dead|archive-url=https://web.archive.org/web/20140210035233/http://www.tfl.gov.uk/corporate/modesoftransport/londonunderground/keyfacts/13175.aspx}}
* [https://www.ltmuseum.co.uk/collections/collections-online/photographs London Transport Museum Photographic Archive]
** {{LTM archive|2002-13461|Promotional map of extension, 1933}} - ([https://web.archive.org/web/20200908172519/https://images.ltmuseum.co.uk/images/max/0c/i0000a0c.jpg Archive])
** {{LTM archive|2002-13443|Diagramatic map showing through trains from Uxbridge to Piccadilly and Cockfosters, 1933}}
* {{cite web |title=The Piccadilly Line – History |url=http://www.krysstal.com/piccline.html |work=www.krysstal.com |publisher=KryssTal |access-date=12 April 2011}}
* {{cite web |url=http://www.architecture.com/LibraryDrawingsAndPhotographs/Exhibitionsandloans/VARIBAArchitecturePartnershipexhibitions/UndergroundJourneys/ChangingthefaceofLondonUnderground/ChangingTheFaceOfLondonUnderground.aspx |title=Underground Journeys: Changing the face of London Underground Illustrated history of the Piccadilly line 1920-1930s |work=www.architecture.com |publisher=[[Royal Institute of British Architects]] |access-date=19 February 2011 |url-status = dead|archive-url=https://web.archive.org/web/20110504024645/http://www.architecture.com/LibraryDrawingsAndPhotographs/Exhibitionsandloans/VARIBAArchitecturePartnershipexhibitions/UndergroundJourneys/ChangingthefaceofLondonUnderground/ChangingTheFaceOfLondonUnderground.aspx |archive-date=4 May 2011 }}

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